OP - your seasonal start date is of course dictated by weather, soil, and turf conditions. For instance in 2011 I didn't start first round until late April. Last year, I started late March. That is a whole month difference and it changes your WHOLE program and way of doing things year by year. What I am saying is, you have to learn to adapt your fixed program to whats going on - in no way will it be rigid.
Also, was going to say that in any season, late May for a pre app is too late (I am a far north applicator as well). You will want to push that up some, and in some early spring seasons, you may be spraying for broadleafs at the same time. Also, use prodiamine not Dimension and if you use Dimension, step up your % active ingredient .10 to me is just like peeing for crabgrass prevention.
You'll want to bump up your Rd's 2 and 3 accordingly.
Also, I would add a 5th round, a late fall straight fert spot spray app.
7x14 Stealth SE Enclosed with 48" side ramp
08 Toro Z400 - 48" deck, 21HP Kaw
09 Exmark Turf Tracer HP 36"
21" Toro SR4 Super Recycler
Stihl KM90 Kombi w/ straight shaft trimmer & tiller heads
Husqvarna 125B Blower
Turfco XT5 Aerator
Turfco LS-22 Overseeder
I can do all things through Him who gives me strength.