Mark Maximum Value In Range Block Based On 2 Columns

I have a long list of stock values (col C) arranged in time blocks so;

CREATE TABLES LIKE BELOW?B C M N

19:00 50.00 0 47.1
19:00 51.00 0 47.5
19:00 52.00 1 48.3
19:00 51.00 0 47.3
19:10 36.00 0 45.3 (nb time has changed)

etc

I need a routine that takes the following action;

When the value 1 occurs in col M row .. (it will only occur once in each time block) and N1 on the same row has the highest value [ 1 and 48.3 above] put 1 in column O on the same row else a 0.

If 1 occurs in column N (time block X) and the value in N is not the highest then store a 0.

This needs to be done for each time block.

It feels like this can probably done by an If or vlookup type of routine but I can't come up with one that works across blocks of times.