At the moment you can only energize the master a few seconds after the first zone (using the so called Master On Adjustment option). You can’t have Master energize before the first zone. There are a couple of work-arounds you can try:
1. Perhaps the 7.5VDC adapter isn’t powerful enough (it’s only rated 1amp). You can try to get a 2amp one (or if your 12VDC supply works, it should be ok, yes the holding current is a bit higher but people have used 12VDC to directly drive their 24VAC valves for years without problem). If you want something in between, try 9VDC.
2. There is a work-around to introduce a delay for master zone. That is to use a dummy zone. To do so, let’s say your master zone is zone 1, and let’s make zone 2 a dummy zone, which means you don’t connect any valve wire to it. When you set a program, schedule zone 2 together in the program, for a few seconds. This way, master zone will turn on together with zone 2, but since zone 2 is dummy, nothing will happen, and when it comes to zone 3, master is already on, so that solves the ‘introduce a few seconds of delay’ request.