stars helper would be an option. But there should be some other options im not familiar with

Also curious about that.

Just by a set of D&D dice and use two d10 to do the same thing. It's just about as quick and can't violate any sites TOC. Or just use your clock: 5% of an our is three minutes. If you need to do some 30% of the time do it when it's between the XX:00 and XX:18, don't do it outside of that range.

If you're on stars, you can use StarsHelper. For other sites, I use Table Tamer - helps sort out your tables, gives you an RNG, hotkeys etc. You can use it for free up to 25NL, or you can use a google RNG if you don't want to pay for it