Hiya!
Gonna try and answer your questions best I can
Dreamfeeds usually happen before 11 pm because they can be the cause of nightwakings if they are anytime afterword. If you want to get real technical about it, the reason it interfears with night sleep after 11 is because it really begins to take its toll on the normal night sleep cycle. Most lo's usually get the majority of their deep sleep, or restorative sleep, during the PM side of the night. The AM side of the night is generally filled with REM sleep, and most of the time nightwakings happen during this time of the night because it's a lighter sleep cycle. REM sleep cycle's generally begin anytime after 11 pm and continue on the rest of the night. Some moms and dads do dream feeds after 11 pm (but not after midnight), and it works fine, but all babies are different as they go into their REM cycles at different times.
As your lo gets older, it's a good idea to start to drop the DF whenever you feel your lo is ready for it, usually around 6 months or so as by this time the majority of lo's usually don't need the nutrition during the night. If you continue to do the dreamfeed, it becomes a habit, as lo's have this nasty ability to realize that "hey...mom and dad are getting me up for a feed, now would be a great time to play with them!"
As for w2s, that would be a great thing to try at this point. The fact that you are able to pinpoint a time when your lo is waking at night is indication that you definately have a nightwaking problem on your hands rather than a hunger problem.
As for getting rid of the feeds, if w2s doesn't work, the watered down feed idea works to. You can try either one, whichever you're most comfortable with. You definately may want to try this in order to begin to drop the DF, which to me sounds like a good idea based on what you're saying.
Good luck tonight!!
*HUGS*
Sonya =P