The journey to our home galaxy will take many hours with your vessel in tow. You may consult your superiors en route.
Technically that could mean days, but the only lengthy gap was when O'neill went off to consult his superiors on Earth. They may have needed a few hours to talk it over, but it's unlikely it took them days to make a decision. The device you're referring to wasn't built by Carter. Rather Thor had it built for her using Earth-based materials. She was probably just studying it when O'neill interrupted her. After that O'neill says he's hungry, goes to cargo by three where the food is, talks to Jonas and Teal'c there, and, as they're talking, they drop out of hyperspace.
Indeed, the BC-304 Class ships just can't generate enough power to really run the Asgard-Systems at their most efficient (The Asgard don't build big ships just because! Their technology needs the room for power-generation! It's the same for the Goa'uld, that's why those Ha'tak can run superior technology, because they generate tons more power than a 304, a stock 304 could never fight a stock Ha'tak and even with the Asgard-Beams it isn't a guaranteed victory if the Ha'tak opens fire first (look at what happened to Sam's ship in the SGU opening episode, it got pounded - Asgard-Weapons offline (because of damage!) etc.)), thus they are slow, have (comparably!) weak shields etc. (I bet even the APBW is stronger or at least able to fire faster with a propper power-source!)