When is a good time and day to use Tinder and dating apps to message girls?

I would say after 5 pm. After work time. That way if the girl is seeing your messages and replies instantly, the conversation will have a good back and forth. But if the girl is replying even during the day, no sweat either

No real time as they all have their own schedules, but Tinder says 6-10PM is usually the pattern when people are on the app. From my experience, when they match with you that's likely the short time window you'll see them on that app. I open them after about a minute or so and then reasonably mirror their texting cadence. If they move fast I soft close and then hard close immediately after and get the number. The pro to this is you got them off the app and you don't have to wait on their response or potentially have them chat with other guys. The con is you lack investment from her so you need to build it quickly after you have her number or she will ghost you.

There's no perfect time to use dating apps, just when it's most convenient to you.

Just open with a decent line that's related to them, and if they're interested they'll respond when they see it.