The generic answer is "It all depends..." on the type of stain, the type if fiber, the exact length of time it sits there.

It's easier to remove a stain when it's fresh or not dried on yet.

If the stain is set (dried), it's best to pretreat with a stain remover and let it sit for a while to let the enzymes do their work (a few hours or overnight).

Exposing the stain to heat will make it impossible or close to impossible to remove.

Like Cavimum said...it all depends.

I would say yes, any stain could be come permanent if it sits long enough. If it's going to be a while before you can actually wash the item, run some cold water on it and squirt some liquid Dawn dish soap and rub a little. That should handle it till you can actually put it in the washer.

So basically, just to be safe, it's better to just wash the clothes right away right?

Sure, if you can. The sooner the better, but it also depends on the kind of stain and material of the fabric. Sometimes it's a goner from the get-go.

And NEVER run it through the dryer until you're sure the stain is gone. Often it's best to air dry the first time to be sure.