How to set the format for a field so user must enter time is a certain format?

format ...

Format is the way data looks ... not what it IS ...  Format can give clues, and trigger other behaviors. It may be good to set the format property to one of the named time formats, or enter a custom format when a Time is expected.  However, this will not stop the user from entering something that is not a valid time.

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to answer your question:

To ensure data can be understood as a Time before allowing the user to leave the control, here are a couple ways:

1. InputMask might seem to be the easy choice ... however, there are reasons I would not set it for date/time ... for instance, to use shortcuts like 8a (8:00 am), and 2p (2:00 pm).

2. validate data using form BeforeUpdate event, and/or control BeforeUpdate event

check the value that the user inputs before it is saved.  If you are new to VBA and need an example, please let us know.

thanks

have an awesome day,
crystal

Yes, I am new to vba, an example would help

actually, you don't need VBA in this case, since the controls are bound to fields.  In the design view of the tblSilica1 table, the data type of [Sampling Start Time] and [Sampling End Time] should be Date/Time, not Short Text.

Internally, Date/Time stores values as numbers; the whole part of the number represents days passed since 12/30/1899; the fractional part of the number represents time.
0.5 is noon -- halfway through the day
0.75 is 6:00 pm

Hate to pile on, but I could not agree more with Gustav. Your database is badly in need of normalization.

Thanks everyone. I have started to normalize the data and have already decreased the table field size form 255 to 190, thank you all

cssc, here is a free book you can read to help you with Access:

Access Basics
http://www.AccessMVP.com/strive4peace
Free 100-page book that covers essentials in Access

be sure to pay close attention to the Normalization chapter.

Thanks