I've tried to search for MIN with multiple criteria, but had difficultly
applying the examples

I record running times, and I want to get the best time for a given day. So
column A has the date, and column B has the number of seconds. Column C
should show the day's best time (so it would be repeated for each row where
the date is the same).

For example, A2:A10 all have today's date. B2:B10 have times in seconds.
If B5 is the fastest time, the time in B5 would display in C2:C10.
Cells A11:A23 have yesterday's date - etc - I need the C2 formula to copy
down.

Thanks in advance

Daniel