There is no better time to start than now! At 3.5 months he should be feeding every 3 hours with about an hour, maybe hour and a half at very most, of waketime. Picking a wakeup and bedtime are KEY things! I think once you get this worked out, you'll see night sleeping get better and better!
If it weren't for a schedule, I would be i-n-sane. No doubt. I have a very sick little one and it's the only thing that keeps me going; knowing that if I can make it until ___, it will be naptime and I can enjoy some quiet.
When Ellie (my youngest) was 3.5 months she was doing this:
7am: wake and bottle
7:45-10am: nap
10am: wake and bottle
10:45-1pm: nap
1pm: wake and bottle
1:45-4pm: nap
4pm: wake and bottle
4:45 or 5-6pm: nap
6pm: wake and play
6:30pm: bottle
7pm: bed
10pm: dreamfeed (
Sleep begets sleep. Ellie was sleeping through the night at 10 weeks (7pm-7am with a dreamfeeding at 10pm). She was totally STTN by 4 months (7pm-7am, no wakings) which is late in my opinion. My oldest was STTN with a dreamfeeding at 6 weeks and totally by 10 weeks. Granted, things are different with Ellie because she's sick and we can't let her cry it out as much.
A dreamfeeding is a feeding late at night. You need to make this one as quiet and calm as possible. No lights, no talking, nothing really. Just feed and put back to bed.
Also note that Ellie's waketime was on the small side. One of her medications has a lot of alcohol in it so she's sleepier than most. I think an hour to an hour and a half of waketime is pretty normal.