The best way to really be sure that some of the eggs hatch is to remove them from the tank. Try to remove what they laid them on into at least a ten gallon or even a 2gal tank with an air stone nearby. Be sure to remove any eggs that appear to be white with a small medicine dropper or even a toothpick.
Try to keep the temperature around 80F. After about 3 days the eggs will hatch. For 5 days the fry feed off their yolk sac and often remain sitting on the bottom. At the end of this period you will suddenly notice them all up and swimming in a tight school. This is the vital time to start feeding them. You must have a brine shrimp hatchery prepared beforehand in order to feed the babies as soon as possible when they become free-swimming. Brine shrimp are not difficult to hatch, all you need is a 1gal container or so with an airstone. You can often find special packets of brine shrimp eggs plus the salt prepared already and all you need to do is add water, keep the hatchery warm at around 80-82F and provide aeration with an airstone.
You can also consider feeding the babies Hikari brand 'first bites' which are made for tiny baby fish, make sure the food sinks into the water so the baby angels can get at it. It's best to feed fry as often as you possibly can. Small and frequent feedings are best for their growth and health. At least 6 times a day is great--if you can manage it.
Make sure to keep the hatchery tank clean and siphon free of any debri, uneaten food or fry that may have died. I use an airline tube to carefully siphon out debri, you must be careful not to siphon out any fry which usually isn't too hard but even if you make a mistake, usually fry are unharmed and can be gently scooped in a small cup and returned to the tank. Use a light colored container for draining the water so you can see any 'mistakes' should there be any.
When I raise my broods of angels, I try to do a 30-50% water change daily on fry tanks, these water changes are great for encouraging good health and excellent growth and keeping a clean tank prevents many of the fin deformities that are often blamed on genetics when in fact it is simply dirty water conditons.
Raising Angelfish babies is a lot of work and time but the reward is a tankful of beautiful little baby angelfish who develop unique colors and patterns to surprise you and they soon learn to rush to the front of the tank in a frenzy whenever their owner approaches!