When I spent one night gardening, to avoid the hot sun, I could not get to sleep until 3 AM! Gardening hypes me up and makes me feel TOO great! For me night time gardening does not help me to sleep.
If this were not so, I would happily spend time in the garden late at might, and I would plant flowers that bloom at night as well. I simply WILT in the hot summer days. But, if I want to get any sleep at night I need to stay inside! Which also makes it pointless to plant night blooming flowers, as I would not (alas) be outside to enjoy them.