hi, first time poster. i really hope someone can help me with this one.

I have a really large sheet of data, 9 columns of data of 10min increments for a period of roughly a year; so its 300000rows.

in this sheet I plan to split data into 6hourblocks and perform a calculation on each block. It is from the result of this calculation that I will brand the block either, stable, neutral, unstable.

I need the rows of data in my second worksheet to 'look' at this first worksheet and match its date and time to the first sheet to determine itself as either stable,neutral, or unstable.
and I'm simply not sure what to do

id really appreciate if someone could help me with this problem

thanks!