Thanks for participating in our answers forum community! I understand that you are experiencing an issue while using the program guide within your SlingPlayer and II'll be happy to help you here.
When changing times/dates the option to return to "Now" appears, and when you click that it restores the date and time to the current date/time. To return to the guide and display the current listings, just click "OK" and this will refresh the guide. I just tested this here in our lab for functionality and it is working properly.
I also haven't heard any reports of this happening to other users. If the issue persists, I would recommend trying a different browser and even another PC or MAC to isolate the issue.
Hope this helps!
The Sling Moderation Team