As you know I am in your region. I think its a bit early for splitting. We are enjoying a so far warm and steady spring (though a slow started one, too), but our nighttime minimum temps are still hovering in the 36-42 range. I would not split unless forced to by unequivocal signs of imminent swarming: you start to see early stage, but definitely charged queen cells on 5-day interval hive tip ups. And if you are also seeing a fair amount of nearly hatched drone brood (or lots of live drones.) Drones take 10 days longer to emerge than queens.
Why not set out to do the box tips on a five-day schedule? (I haven't started mine though I may do so next weekend, certainly by the following one.) With only two boxes to check it should take you less then 10 min/hive. Twenty minutes every five days is not an onerous chore. If you see charged queen cells on the bottom of the frames you will know it's time. I scrape all queen cups off the bottom of the frame so I know I am not missing anything each time. (I know they will replace them with in hours.)
Also, just take one of the "excess pollen frames" (starting with the oldest and skankiest one) to make way for opening the side of the brood nest. Take another one out once they start to draw the first OSBN, which will happen in about 6-12 days. Freeze the frames you take out so SHB don't start in on them. They are still useful to the bees, just not so much right now. I rarely do more than three rounds of it.
Also checkerboarding as a swarm-prevention technique requires drawn comb both with stores and without. if you don;t have that it cant be done. Make a point of getting some extras made this summer for next spring. It is started much earlier than this, so it is too late for a Walt Wright style checkerboarding project , even up here . Also get ready to super up with drawn comb so that when the dandelions start they don' have to store choose between brood and nectar storage.
Do you know how to do the tip ups and what to look for? Quick and easy for you, and easy on the bees.
Nancy