Set Focus, Validate data?

[Blondie96]

I have a form that accepts

BegDate1 BegHour1 EndDate1 EndHour1
BegDate2 BegHour2 EndDate2 EndHour2
BegDate3 BegHour3 EndDate3 EndHour3
BegDate4 BegHour4 EndDate4 EndHour4
BegDate5 BegHour5 EndDate5 EndHour5


I am trying to validate data & force re-entry of the field if it does not
pass. I have only been able to use the setfocus from within the onfocus of
the next field, resetting it to the previous field.

Is there a way to check before leaving the field & stop the focus from
moving to the next field.

Reason:

I can enter 1 to 5 requests each with a start & end Date & time. I need to
check that end time in each row before it tries to go to the next field
because the user may not go to the next field. If a time does not pass the
criteria I want to force re-entry of that field.

Can someone help me with this please.

Thanks,
Tamra