Hey Richard,
This is the first year I put my feeders up real early.
I put them up in mid April, once they were sighted in Southern Ontario.
I've had hummers since the 2nd week of May, but not constantly.
Ususally I don't put them out till later in the summer, when they are around all the time.
This year I thought I would try and get them out early to entice the hummers to stick around my yard for the whole season. But they have their routine and it is the same amount of traffic as if I didn't have them out at all.
So you'll probably be ok.
At my place Spring and early Summer is kind of hit and miss, right now I have 1 male fairly regularly.
By the end of the month and staight through till early October it is a constant stream of hummers, with 4 or 5 buzzing around my very small backyard at one time.
I don't see any problem with putting them out now, this is the time of year I sometimes do, and I'll have hummers till the fall.
Also, you never really know what is buzzing around your backyard when you are not around. It's all in timing.
I sat outside on Sunday for 5 hours waiting for one to buzz in and nothing. So I went inside to get dinner ready, I took 2 steps inside the house and then realized I had forgotten to grap something from the table on the deck. I turned around to go back to the door and there was the male on the feeder. Would never of seen him if I didn't turn back around.
My point being is they are around, but like all other things when it comes to birding, is they are never around when you are.
So put them out, keep the necter fresh and you'll get them. Even if they don't find your feeders till later on in the season, they'll stick around till at least September. Also, if you get them this year, they'll be back next year. They will return to a place with feeders every year.
Good Luck
Meghan