How long after the first guinea pig is born will the next one come out?

It kinda depends on how many babies the mother had and how old the mum is if she only had a few like 1 or 2 maybe even 3 and your mum was a big enough to have them without giving birth premature they should be fine. The babies can eat solids after a couple of hours but they will not want to so make sure the sow (mum) is producing enough milk. If not or you are worried about it you can always buy some evaporated milk and feed to babies through a dropper but do not squezze the dropper when feeding because the babies will inhail it and die just leave a small drop on the tip and the babies will suckle to get the milk out. If your babies are under 60g do this every 2 hours until over 60g every day and night