I would suggest that you read the label on the bag of feed. It should give you all the information you need with regards to this question.

You should see results pretty quickly if the feed has been rained in. So much depends on the weather! Once the fertilizer has been well soaked in a dry spell shouldn't hurt but all grass grows more slowly in dry weather anyway.
It is much better to use a slightly longer cut more frequently than a short one less often but a good general rule is to cut it when it looks as though it needs it. Cutting on the shortest cut will tend to weaken the grass as there is less leaf to feed the roots.