diff --git a/README.md b/README.md
index 0714c48..d2b46f4 100644
--- a/README.md
+++ b/README.md
@@ -9,8 +9,9 @@ level of precision is better left to other tools.
 
 ## Source Configuration
 
-* `interval`: *Optional. Required unless `start` and `stop` are defined.* The
-  interval on which to report new versions. Valid examples: `60s`, `90m`, `1h`.
+* `interval`: *Optional.* The interval on which to report new versions. Valid
+  examples: `60s`, `90m`, `1h`. If not specified, this resource will generate
+  exactly 1 new version per calendar day on each of the valid `days`.
 
 * `location`: *Optional. Default `UTC`.* The
   [location](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones) in
@@ -22,10 +23,12 @@ level of precision is better left to other tools.
   location: Africa/Abidjan
   ```
 
-* `start` and `stop`: *Optional.* Only create new time versions between this
-  time range. The supported formats for the times are: `3:04 PM`, `3PM`, `3
-  PM`, `15:04`, and `1504`. If a `start` is specified, a `stop` must also be
-  specified, and vice versa.
+* `start` and `stop`: *Optional.* Limit the creation of new versions to times
+  on/after `start` and before `stop`. The supported formats for the times are:
+  `3:04 PM`, `3PM`, `3PM`, `15:04`, and `1504`. If a `start` is specified, a
+  `stop` must also be specified, and vice versa. If neither value is specified,
+  both values will default to `00:00` and this resource can generate a new
+  version (based on `interval`) at any time of day.
 
   e.g.
 
@@ -37,8 +40,19 @@ level of precision is better left to other tools.
   **Deprecation: an offset may be appended, e.g. `+0700` or `-0400`, but you
   should use `location` instead.**
 
-* `days`: *Optional.* Run only on these day(s). Supported days are: `Sunday`,
-  `Monday`, `Tuesday`, `Wednesday`, `Thursday`, `Friday` and `Saturday`.
+  To explicitly represent a full calendar day, set `start` and `stop` to
+  the same value.
+
+  e.g.
+
+  ```
+  start: 6:00 AM
+  stop: 6:00 AM
+  ```
+
+* `days`: *Optional.* Limit the creation of new time versions to the specified
+  day(s). Supported days are: `Sunday`, `Monday`, `Tuesday`, `Wednesday`,
+  `Thursday`, `Friday` and `Saturday`.
 
   e.g.
 
diff --git a/check/check_test.go b/check/check_test.go
index b374520..378df50 100644
--- a/check/check_test.go
+++ b/check/check_test.go
@@ -60,6 +60,44 @@ var _ = Describe("Check", func() {
 			Expect(err).NotTo(HaveOccurred())
 		})
 
+		Context("when nothing is specified", func() {
+			Context("when no version is given", func() {
+				It("outputs a version containing the current time", func() {
+					Expect(response).To(HaveLen(1))
+					Expect(response[0].Time.Unix()).To(BeNumerically("~", time.Now().Unix(), 1))
+				})
+			})
+
+			Context("when a version is given", func() {
+				var prev time.Time
+
+				Context("when the resource has already triggered on the current day", func() {
+					BeforeEach(func() {
+						prev = time.Date(now.Year(), now.Month(), now.Day(), now.Hour(), 0, now.Second(), now.Nanosecond(), now.Location())
+						version = &models.Version{Time: prev}
+					})
+
+					It("outputs a supplied version", func() {
+						Expect(response).To(HaveLen(1))
+						Expect(response[0].Time.Unix()).To(BeNumerically("~", prev.Unix(), 1))
+					})
+				})
+
+				Context("when the resource was triggered yesterday", func() {
+					BeforeEach(func() {
+						prev = now.Add(-24 * time.Hour)
+						version = &models.Version{Time: prev}
+					})
+
+					It("outputs a version containing the current time and supplied version", func() {
+						Expect(response).To(HaveLen(2))
+						Expect(response[0].Time.Unix()).To(BeNumerically("~", prev.Unix(), 1))
+						Expect(response[1].Time.Unix()).To(BeNumerically("~", time.Now().Unix(), 1))
+					})
+				})
+			})
+		})
+
 		Context("when a time range is specified", func() {
 			Context("when we are in the specified time range", func() {
 				BeforeEach(func() {
@@ -533,15 +571,6 @@ var _ = Describe("Check", func() {
 			Expect(err).NotTo(HaveOccurred())
 		})
 
-		Context("with a missing everything", func() {
-			It("returns an error", func() {
-				<-session.Exited
-
-				Expect(session.Err).To(gbytes.Say("must configure either 'interval' or 'start' and 'stop'"))
-				Expect(session.ExitCode()).To(Equal(1))
-			})
-		})
-
 		Context("with a missing stop", func() {
 			BeforeEach(func() {
 				source["start"] = tod(3, 4, -7)
diff --git a/lord/time_lord.go b/lord/time_lord.go
index fbe1086..e6890f7 100644
--- a/lord/time_lord.go
+++ b/lord/time_lord.go
@@ -2,9 +2,12 @@ package lord
 
 import (
 	"time"
+
 	"github.com/concourse/time-resource/models"
 )
 
+var DEFAULT_TIME_OF_DAY = models.TimeOfDay(time.Duration(0))
+
 type TimeLord struct {
 	PreviousTime time.Time
 	Location     *models.Location
@@ -59,23 +62,28 @@ func (tl TimeLord) daysMatch(now time.Time) bool {
 
 func (tl TimeLord) latestRangeBefore(reference time.Time) (time.Time, time.Time) {
 
-	if tl.Start == nil || tl.Stop == nil {
-		return time.Time{}, time.Time{}
+	tlStart := DEFAULT_TIME_OF_DAY
+	if tl.Start != nil {
+		tlStart = *tl.Start
+	}
+	tlStop := DEFAULT_TIME_OF_DAY
+	if tl.Stop != nil {
+		tlStop = *tl.Stop
 	}
 
 	refInLoc := reference.In(tl.loc())
 
 	start := time.Date(refInLoc.Year(), refInLoc.Month(), refInLoc.Day(),
-		tl.Start.Hour(), tl.Start.Minute(), 0, 0, tl.loc())
+		tlStart.Hour(), tlStart.Minute(), 0, 0, tl.loc())
 
 	if start.After(refInLoc) {
 		start = start.AddDate(0, 0, -1)
 	}
 
 	stop := time.Date(start.Year(), start.Month(), start.Day(),
-		tl.Stop.Hour(), tl.Stop.Minute(), 0, 0, tl.loc())
+		tlStop.Hour(), tlStop.Minute(), 0, 0, tl.loc())
 
-	if stop.Before(start) {
+	if !stop.After(start) {
 		stop = stop.AddDate(0, 0, 1)
 	}
 
diff --git a/models/models.go b/models/models.go
index 100ed42..6a97694 100644
--- a/models/models.go
+++ b/models/models.go
@@ -47,10 +47,6 @@ type Source struct {
 }
 
 func (source Source) Validate() error {
-	if source.Interval == nil && source.Start == nil && source.Stop == nil {
-		return errors.New("must configure either 'interval' or 'start' and 'stop'")
-	}
-
 	if source.Start != nil && source.Stop == nil {
 		return errors.New("must configure 'stop' if 'start' is set")
 	}