I put my fleece down on 3 and a half beds on March 13th, being away for 8 days when it did rain sufficiently not to need watering.
I came back and the direct sown turnip rows had all germinated beautifully, the bed where I sowed forcing carrots germinated weeds spectacularly (that compost must have had a low temperature initial pile!), the beetroot had established well in 7/10 clumps (so I replaced three with the back ups), the spinach and cabbage had been munched despite the outdoor back ups in pots growing on beautifully and the radish, onion clumps and spring onion clumps looked fine.
Does tell me that even fleece does not guarantee success if you push the boundaries….