Assuming it is a Medium Time (i.e. 8:00 AM or 4:00 PM) do not set this in the form. In the query make an additonal field and add the following TimeText: Right([Timefield],2) in the criteria add [What time of day?]
If you need to do this in the form add the following to the AfterUpdate event of Field 1
me.field2 = Right([Field1],2)
make sure that the Format of field 1 is set to a Medium Time (8:00 AM, 12:00 PM, 3:00 AM, etc)
HTH