As a (currently diet only) T2 I generally check m fasting level first thing in the morning, then immediately before and two hours after each meal to see what, if any, impact the carbs I've eaten have had on my glucose levels. If I feel it necessary /useful I may also i do some extra checks if I ever have to take different meds, if I'm ill, or very stressed. I used to check 1 hour into meal if I thought I might go extra high then.
When I wore a Libre sensor I used the Reader every 8 hours to collect its data, and at meal times to see how the reading and any meal time finger pricks corresponded, I learned more from this regarding how food in different combinations affected me, than than I did from doing the pre & post meal pricking, and (possibly more informative) how non food related issues could often have a much bigger impact on my glucose levels.