It really depends on the condition of the field and the growth. There is no health reason why it can't be grazed straight away, however they are usually harrowed to spread the dung (after winter grazing) and ariate the ground. So ideally left long enough to kill off worm eggs etc which have been spread after harrowing. Rolling is really to flatten the ground and get rid of the ruts. So if the grass is growing and re-established no reason you can't graze it. If you have cut grass/ topped fields it should be left for a few weeks before grazing. I hope that helps to answer the question 😳
We also get ours used to tractor in the field with equipment. Mind you my 3yo Cupcake thought it was great craic. Reared up in front of tractor, came down, and stood in front of tractor as if to say bring it on.
However, after harrowing and rolling was done mine were in sacrafice paddocks for about 5 weeks. I put seaweed down and sprayed. The fields needed maintanence and it also rained a lot again. Been back on about a week. Night grazing for 12 hours. In sacrafice paddock for 8 and in for 4 hours in the evening. Mine like to take this time to sleep flat out.