I am converting an application from Oracle Forms 6i to 10g, one of the fields has a date format of MM/DD/RR HH24:MI. QA noticed that in 6i you can type 01/01/13 1645 without the colon in the middle of the time and 6i forms would understand it. Forms 10g displays an error... FRM-50025: Date/time must be entered in a format like MM/DD/RR HH24:MI.
Out of curiosity, I created a little test form in Forms 6i with your format mask. Running it, I can enter the date and time without the / or :, and all works fine. As soon as I leave the field, Forms automatically re-displays the date and time with the correct punctuation.
Then I compiled that form in Forms 10g and ran it. It works just the same.
There are some internal format mask elements that may have been set for your Forms 10 installation. If you search online help for format mask, you can read a lot. ....more than I want to see.
I am using a plain vanilla installation of 10g: version is 10.1.2.3.0