A 10" basket or container will usually bloom steadily until end of July, if fertilized and watered regularly. The larger the size of the basket the longer the plant will bloom as it has more room to grow.
If you plants stops flowering, gets leggy or sparse you can trim it back to about 3" from the rim of the basket. Place the basket in a part sun / part shade area and give it careful watering and fertilizing as it needs. This will help it grow back into fullness.
Another option is to transplant your basket or container into a larger pot. This will give the plant more room for root space thus better branching and flowering :) A trim will also be helpful clean up any leggy branches in this situation.