You don't really need to count to 7 if you just use Han's basic, but if you want to use his moddle special, you don't want to do that on the 7th hit. There's also the issue of if you want to save CLS middle special if 7th hit is coming up. I'd say speed is your biggest concern.
If you have Dathcha 7*, you could throw him in with just enough gear to use his leader ability, and that will help your tmr.
If using undergeared CLS/Zolo, if found that adding not only Datcha lead but also Rex and QGJ could help me clear phase 1 still. As CLS and Zolo got better gear I removed first QGJ, then Rex later.
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Your attack damage happens, grievous goes to 100% tm, any tmr goes through.
If you have Dathcha 7*, you could throw him in with just enough gear to use his leader ability, and that will help your tmr.