IMO you are putting him to bed (doing the nighttime routine) too early. 4pm seems very early to me to be starting the bedtime routine and settling down for the night. 4pm til 4am is 12 hrs so I'm not really surprised that he is waking up then.
I haven't read or know anything about 'Save our Sleep' but I would probaly be waking him, feeding and having a little play (nothing too stimulating of course) at about 7pm till about 8pm. Dropping the 9pm and midnight feeds for a 10 or 11pm dreamfeed. I would not want to have to stay up until midnight to be doing any feeds (unless it is your DH doing it) you really need to be in bed before that! I would expect to still be feeding a 3month old overnight and that may very well be at 4am! Personally we were still feeding overnight until around 7mths then we had a bad patch from about 8mths until about 9mths and now we are generally sleeping thru at 12mths!
HTH