I don't know if you've noticed it, but the days are slowly getting shorter each and every day. It started just after the first day of summer (solstice). However, for what it's worth, the warmest time of the year is generally in August, at least a month and a half after the longest day of the year.
Explanation...the land, ocean and atmosphere of the earth take time to warm up in response to solar heating. And the opposite is true during the winter. Winter begins before right before Christmas. However, the coldest air of the season generally comes in February.
If you want to see how much earlier the sunset is getting each day, check out http://aa.usno.navy.mil/data/docs/RS_OneYear.php.