The time to change is usually when they start taking a very long time to finish a bottle or give up after a while. A bottle feed should be done within about 20 mins and there should be enough in the bottle so they can stop when they are finished and not just because the bottle is empty. When you change teats there can be a bit of spluttering for a few feeds while they get used to it so I would try the no2 for a day and if he is still spluttering after a good few feeds he may not be ready for it yet.
With the nightfeeds even if you do get a bit more in during the day he is going to need it for a good while yet. The dreamfeed is usually dropped around 8 months when solids are established and most babies need a nightfeed during their first 6 months. Remember their tummies are tiny and they need the calories for all the growth spurts (usually 3 weeks, 6 weeks, 12 weeks, 4 months and 6 months and sometimes inbetween!). Some babies do sleep from DF to wake up without a nightfeed earlier but it's their choice rather than an active wean of the the feed.
HTH!
Laura