wrote:
Column A contains a start date
Column C contains an end date
[....]
Column B contains a start time
Column D contains an end time
What I need is a formula to compute the hours and minutes
between the combined start date and time and the combined
end date and time.

=(C2+D2)-(A2+B2)

formatted as Custom [h]:mm .

The [h] form displays hours greater than 24, if appropriate.