It’s just what it is. You only pay for the first mix, that’s why that one goes through fast. After that you’ll have to wait. It’s a trade off compared to Wasabi but you get more mixes for the same price if you want. Theoretically you can mix forever. I was waiting for 2 months to get 7 to 8 mixes for each UTXO. It were like 20 UTXOs or so if I remember correctly