Totoro,
We went to about 11 bridal shops in all before deciding. On average, if they let you try the gowns, you should allow 45 minutes each. Call for an appointment first. Not every place will let you try their gowns. And many will hard-sell you. Beware.
You should look into the bridal boutiques thread of this forum before you go, and shortlist a few. Tanjong Pagar is just full of them. It's along Tanjong Pagar Rd, not far from Maxwell Rd market. Some are in the street behind Tg Pagar too. They occupy those restored conservation shophouses.
Along Tg Pagar, we went to Julia Wedding News (hard-sell), La Galleria and a few others I cannot remember the names already. Make an appointment for better service.