Hi,
Firstly, it is a good idea to give the user an indication as to how the data is to be inputted.
One way is to use the Tooltip in the accessibility panel. Here you can input an explanation of the field and how to input the data. Secondly you can place static text (in a smaller font) beneath the field, which would look like "e.g. 15h00".
The time patterns are available for:
"Display" = setting how the time will look after the user tabs out of the field;
"Edit" = setting how the data will look when the user is editing it;
"Validation" = setting rules to check the time as inputted to see if it conforms to the pattern. If it does the user can tab out of the field, if it dosen't then an error message will come up.
"Data" = setting if you are merging / importing data into your form.
In you case, the minimum requirement would be to set the display pattern to time{H'h'MM}. This means that if the user inputs 1500 or 15:00, it will appear as 15h00 when the user tabs out of the field.
You could also set the edit pattern to time{H'h'MM}, which would mean that when the user goes back into the field it would stay at 15h00. If you do not set the edit pattern when the user goes into the field the time would revert to 15:00 during editing and then back to 15h00 when they exit the field.
Lastly you could set the validation pattern to time{H'h'MM}, which will only accept time inputted as 15h00.
I don't think you need the data pattern, as you propably will not be importing/merging data.
Another solution which might work better if you are assigning fixed periods of time (say 1/2 hour slots during the day), would be to replace the time field with a dropdown list.
In the Object/Field panel you can assign values to the dropdown list, for example:
14h00 to 14h30
14h30 to 15h00
15h00 to 15h30
Then when the user is filling in the form, they have (what looks like) a dropdown for the calander and a dropdown for the time period.
For reference, the help file within LC Designer is good, also there are reference documents on the Adobe website for Javascript and Formcalc.
I would recommend JP Terry's book on LiveCycle. It deals with scripting, but also the principles of good form design.
Hope that helps,
Niall