The A time is about 2 hours. She is able to go on a 4 hour routine, but I've been trying to cluster feed a bit later in the day so I fit in a 5th feed hoping that she might sleep better through the night (yesterday she ate around 7:15, 11:30, 3:30, 6:15 and 7:45 (7 oz for the first 3 and 5 oz for the last 2). I know the routine is a bit unorthodox right now but we just got her back from staying with her grandparents for a week and we're working on getting back on track and trying to figure out what will work for her right now. Her nights vary, last night waking at 2, 4 and 6 going right back to sleep with paci. The night before then, wake at 3:30 and awake babbling for 2 hours, then nap until I woke her at 7. She does not need to eat at night. We're trying to tweak her bedtime and see what will work best.
The dr's reason for starting solids at 4 mos was that her calorie demands will start to outweigh what the formula can provide and to keep her growing she'll need the extra intake. I even told him everything I've read says to wait until closer to 6 mos, but he would hear none of it. When I got home I double checked with WHO and the Canadian Pediatric Society, and they both say to wait till 6 mos!
I think you're right though, I'm sure she'll give me some signs when she's ready for it and I'll just wait until then probably.