I always leave them on longer than the instructions say. If it says 60-90 minutes, I’ll do a minimum of two hours.
Soak your feet each night for a bit in hot water. That’ll speed the peeling process.
From personal experience, Holika Holika’s and TonyMoly’s were really good. Skinfood’s Sparkling Mint one was a LET-DOWN. So disappointing. I also tried like 2 different Japanese ones (I can’t recall the brands) that were okay.