in an empty column put a list of the day - no times - that are in your other column. then enter this formula in the next column and copy down.
{=MAX($B$2:$B$204*N(($A$2:$A$204>=E2)*($A$2:$A$204<E3)))} array formula
I have the date/time column as A and the corresponding number to max in column B.
This will give you a list of max amount by day.
I assume column A contains nothing but your hour readings and the first reading in A1 (you can adapt the formulas to your actual data).
B1 =IF(COUNT(A:A)>0,MAX(A1:A24),"")
B2 =IF(COUNT(A:A)<>COUNT($B$1:B1)*24,MAX(INDIRECT(CONCATENATE("A",COUNT($B$1:B1)*24+1,":A",ROW()*24))),"")
Copy down the one in B2 as far as needed.
You can use the above formulas until someone has something better on offer.
Aladin