Compost used as a mulch isnt going to hurt muture plants..

Water early or late, if your overhead watering with sprinklers, if you have surface drip hoses, I dont think it would matter all that much.

What happened that cuased rot? Sorry if I missed that thread.

flowergirl, mine are doing the same thing. Cleaned them up and I watered mine. The ground had 2" cracks. The temps were cooler (80) and figured they can't get any worse than they were. The temps are in the 90's again, but so far they are doing good.

I would make sure they are mulched, but not too heavily around the crowns. Regular, early morning watering will keep them cooler during the day but prevent fungal problems. Soaking the plants in this heat runs the risk of them cooking later in the day. They need moisture, but also air in the root-zone to stay cool.
I would be afraid of working anything into the soil at this time. Too much danger of cutting roots and giving pathogens a way in. Wait till temps cool in early fall. Ed