If it makes you feel any better I had the exact same anxiety moving here. We moved here in August and my son is a Kindergartener at SAS. We live in Bukit timah but his bus ride is about 40 minutes. I lost sleep over this bus thing. It is REALLY not a big deal at all. The kids are fine and most bring a DS or books on the bus or just chat with other kids.
School starts at 8 and they are home by 3:40. A long day but I have nothing but great things to say about the school and staff. My son loves it there. Hope this helps.
Call Yeap bus service and they can tell you exactly how long it will take from your condo and what pick up and drop off times are.