I've only made two starters (on stir plates) and they didn't make any foam at all, except maybe a layer of bubbles like you'd get on a cup of coffee pouring from the carafe. You should watch it for sure, but I've heard that most starters don't really form much foam.
A starter is usually done by 36 hours, you could probably get away with 24 if you were in a rush, then crash it overnight if you can before decanting. I used a 1gal jug last time, and ended up actually siphoning the beer off the yeast instead of trying to tip it and decant it. Personal preference. If you aren't decanting, you can pitch the 2nd step at high krauesen (even though I'm not sure it will form one) pretty much anytime after a few hours. Some people do their starters in the morning and pitch that day.
If you have time, start one tonight, put it in the fridge Saturday morning, decant it and pour in a new batch of wort Saturday night, and pitch it Sunday when you brew (if that is in fact your brew day). If not, let it go until Sunday evening, then put it in the fridge and pull it out the morning of your brew day to let it come up to pitching temp (or decant it when it comes out).
Got less time? Start 1L tonight, put it in the fridge tomorrow night, decant and add your 2nd step (another 1L) Saturday morning, then pitch it Saturday afternoon. Everything helps.
If anybody else has a better method or better advice, feel free to correct or improve.