Please go back to 600 credits forever
Honestly, for the first time since I got this app, the quantity of free credits seemed fair. I don't know the reasoning behind the temporary increase, but I believe it should be a standard. Players will feel more rewarded, and more comfortable with the idea of paying for credits. Spending money out of necessity always feels like we're paying to live (which is literally the same as paying taxes), but under a more rewarding system, we'd be paying because the devs are treating us well, encouraging us to support it. I say this out of experience. I play FGO, and I never feel the need to pay in order to enjoy the game. The devs of that game make players feel comfortable, so from time to time, when my wallet allows me to, I spend money on the in-game currency to support them. Because the game is fun and I want it to continue existing.
I don't know if I explained myself, but my point is that the money you're bound to receive more money in the long run if you give players a reason to stay by treating them more fairly. Make them love what you do.
So in a long story short, 600 daily credits should be the norm, and players will certainly appreciate it. If not, then 500 credits, at least.