So the answer is
0200 - 0500 is 1010
0500 - 0800 is 1011
0800 - 1100 is 1012
1100+ is 1013
give or take a minute with linear interpretation between.
So at 0200 the QNH is 1010
At 0300 the QNH 1010.33 so you use 1010.
At 0400, you are two thirds of the way in so the QNH would be 1010.67. Do you use 1010 or 1011?
There are people who will say that QNH must always be rounded down but is there a reference?
At 0430 the QNH is 1010.83. What do you use now.
The answer is almost never Quite clear.