The main thing is you don't want the new shoots to grow inside the mulch, then be all spindly and blanched when you uncover them. If this is starting to happen you are pretty much forced to take the protection away - it is a question of balancing the risk of tender new shoots being destroyed by any returning or continuation of winter that might be expected there vs. having them burn up in the sun because they started growing in the dark, were left too long without being uncovered.

And.............unfortunately, the only way of knowing is to remove the collars & mulch now---but I wouldn't be putting them back on that's for sure.

I suggest removal with this big warm up coming. They will be growing and will canker if kept wet.