With rain likely coming the urea will have an effect and will (likely) be effective. As for the seedheads......here is a general explanation of seedheads..... The formation of seedheads effectively curtails continued vegetation growth and regrowth of any grass for that grazing season (I'm saying you should have clipped the seedheads right when/as they were forming. The seedheads send a hormone to the rest of the plant that says 'hey, you have reproduced for the year, you can slow down or stop growing'. At this point, that message has been delivered. Clipping the seedheads at this point may entice some growth, but I suspect the response will be muted. The fact that the seed heads were left on also possibly/likely means that the boost from fertilizer or urea in growth will also not be as strong as desired. I'm not saying don't clip and don't apply urea or fertilizer. I am saying to expect a muted response by the plants as the grass went to seed, which has an effect on plant growth if you do clip and/or fertilize.