One crowd calendar is showing February 21 as 6/10 and February 26 as 4/10.
Another shows both of those days as "slow."
My
personal plan of attack would be to show up 20 minutes or so before the park officially opens and then head right to the WWOHP area of the park as soon as you're let in. Check the wait times for the major attractions and if they're doable, go ahead and hop in line. In my experience, things DO slow down most evenings, but you also don't want to bank everything on that and have it end up being an evening where things never really let up!
You can use Universal's mobile app to track wait times throughout the day as well.
I highly recommend adding the park-to-park option to your tickets. It'd add $45 per person to the cost, but I think it's well worth it to have access to BOTH parks all day long on both days. Not only is the Hogwarts Express pretty great, but it's also a really convenient way to hop back and forth between the parks throughout the day!
I'm sure other peeps will chime in as well....