How do i make splash potion of weakness without wasting hours?

If you want it to last longer, add redstone to the bottle before the gunpowder goes in. Dragon's breath turns the splash one into a lingering cloud if you ever need it.

it's the one that skips nether wart completely - water bottle, fermented spider eye, and that's weakness already brewed. gunpowder in after that turns it splash. if the stand is doing nothing at all, check there's blaze powder in the fuel slot, easy to forget when it's the only potion you've ever made.