diff --git a/ghost/admin/app/components/editor-labs/modals/publish-flow/confirm.js b/ghost/admin/app/components/editor-labs/modals/publish-flow/confirm.js
index 481d100e4a..668a5eabff 100644
--- a/ghost/admin/app/components/editor-labs/modals/publish-flow/confirm.js
+++ b/ghost/admin/app/components/editor-labs/modals/publish-flow/confirm.js
@@ -51,7 +51,7 @@ export default class PublishFlowOptions extends Component {
         try {
             yield this.args.saveTask.perform();
         } catch (e) {
-            if (e === undefined && this.publishOptions.post.errors.length !== 0) {
+            if (e === undefined && this.args.publishOptions.post.errors.length !== 0) {
                 // validation error
                 const validationError = this.args.publishOptions.post.errors.messages[0];
                 this.errorMessage = `Validation failed: ${validationError}`;
diff --git a/ghost/admin/app/utils/publish-options.js b/ghost/admin/app/utils/publish-options.js
index d60b59ba9e..d7b3f66466 100644
--- a/ghost/admin/app/utils/publish-options.js
+++ b/ghost/admin/app/utils/publish-options.js
@@ -41,7 +41,7 @@ export default class PublishOptions {
     @tracked scheduledAtUTC = this.minScheduledAt;
 
     get minScheduledAt() {
-        return moment.utc().add(5, 'minutes');
+        return moment.utc().add(5, 'minutes').milliseconds(0);
     }
 
     @action
@@ -59,11 +59,15 @@ export default class PublishOptions {
 
     @action
     setScheduledAt(date) {
-        if (moment.utc(date).isBefore(this.minScheduledAt)) {
+        // API only stores seconds so providing non-zero milliseconds can
+        // trigger unexpected validation when updating scheduled posts
+        date = moment.utc(date).milliseconds(0);
+
+        if (date.isBefore(this.minScheduledAt)) {
             return;
         }
 
-        this.scheduledAtUTC = moment.utc(date);
+        this.scheduledAtUTC = date;
     }
 
     @action
diff --git a/ghost/admin/app/validators/post.js b/ghost/admin/app/validators/post.js
index 02d3a8633f..716abdc147 100644
--- a/ghost/admin/app/validators/post.js
+++ b/ghost/admin/app/validators/post.js
@@ -185,9 +185,7 @@ export default BaseValidator.create({
         if (isEmpty(model.errors.errorsFor('publishedAtBlogTime'))) {
             let status = model.statusScratch || model.status;
             let now = moment();
-            let publishedAtUTC = model.publishedAtUTC;
             let publishedAtBlogTZ = model.publishedAtBlogTZ;
-            let matchesExisting = publishedAtUTC && publishedAtBlogTZ.isSame(publishedAtUTC);
             let isInFuture = publishedAtBlogTZ.isSameOrAfter(now.add(2, 'minutes'));
 
             // draft/published must be in past
@@ -195,9 +193,8 @@ export default BaseValidator.create({
                 model.errors.add('publishedAtBlogDate', 'Must be in the past');
                 this.invalidate();
 
-            // scheduled must be at least 2 mins in the future
-            // ignore if it matches publishedAtUTC as that is likely an update of a scheduled post
-            } else if (status === 'scheduled' && !matchesExisting && !isInFuture) {
+            // scheduled must be at least 2 mins in the future when first scheduling
+            } else if ((model.changedAttributes().status || model.changedAttributes().publishedAtUTC) && status === 'scheduled' && !isInFuture) {
                 model.errors.add('publishedAtBlogDate', 'Must be at least 2 mins in the future');
                 this.invalidate();
             }