Is it too late to top grazing ground?

Have around 6 acres of reasonably dry ground that is sheltered and I let ewes into to lamb outdoors in Springtime.
Have ewe lambs in grazing off rough grass off it at mo.Intend on leaving it idle from this weekend and putting a bag to the acre of 18:6:12 on it to boost building a bank of grass in it.
Had planned to clean it off a week ago but the really heavy rain we have had stopped that idea as like most land in NW it is saturated at mo.
Couple of dry days would soak it out though.

Has some rushes and thistles and nettles etc on it.Based in Mayo here so our growing season would not last as long as further South.Is it gone a bit too late for cleaning off ground like that?.....would it effect the regrowth rate too much or would it be better left alone with just the fertilizer put out on it?
Appreciate any thoughts.

Ps- would be cleaning off with a disc mower with skids fitted to not cut the grass too close to the ground.