+1, but may I suggest an alternate title? ‘Nighty Night” to me implies sleep-related images; maybe something like “They only come out at night” or “Nighttime activities” or just plain “Night photography.” I don’t really feel strongly about it, and it is your theme, so of course you’re welcome to ignore that and keep your title as well. 🙂
If you do decide to change the title, “Night Photography”, “All Night Long” and “Middle of the Night” have already been used and are classic themes. Middle of the Night is actually quite similar to this but it didn’t have the difficulty. If you want to use either title we can make it a classic theme with your difficulty.