Recently I had some issues with the Android version of Collector when using date/time formats that displayed seconds. Since this was corrected in the 10.2.6 Android update, I left the "12/21/1996 6:00:00 PM" formatting in one of my maps. However, this setting limits the iPad version of Collector to only enter the date when updating this field; the time option is no longer displayed.
When I set the "12/21/1996 6:00:00 PM" time/date format to "12/21/1996 6:00 PM" (removing the seconds), the iPad version then allows the user to update both date and time.
The Collector version for iPad being used is 10.2.5.