Excel tells me that E3=4 is FALSE, where E3=4:45, a time format, and
formatting should be ignored.

The whole formula I'm trying to work out is: =IF(E3=4,"DONE",(4-D3)).
Excel accepts this but reads 4 as 24 and returns 19:15 for (4-D3).

OK, so (E3=4) is FALSE if 4=24, but why does Excel read 4 as 24? And how
do I get Excel to read 4 as 4:00 and return the difference between 4:00 and,
say, 3:27?