Hi!
I don't think there is an exact amount of awake time. It is not uncommong when transitioning, to be tweaking EASY a little bit and be feeding before a nap until her awake time can handle the "ideal" 4 hour routine. And that's ok as long as not feeding her to sleep/can sleep independently

Here are some signs of needing to transition:
1. Not taking as much at a feed (baby not as hungry at 3 hours...or in your case 3.5 hrs :wink: )
2. Erratic Night Wakings
3. They are extending their awake times
4. Starts taking 45 minute naps