2022 guide.
Doing this without boosting, I had the most success finding players on weekend evenings/nights US time. Plenty of matches found, however most players are high-ranked (A or above). Don't expect to get any wins, this is just the best time I've found to grind out 100 matches played.
If you are boosting this with a partner on TA, avoid US evening/nights and avoid weekends for your session, and know what connection quality your boost partner has so you can quickly tell if you matched with the wrong person. Communication and patience is key for boosting.