First Night Swim

Last night I did my first night swim. I planned on doing this workout, but the first 50 meters felt a bit difficult - so I just did 50s with 10-20 second breaks - and focused on my form for about 20 minutes. Then I did 2 100s, a few more 25s and called it a night after 30 minutes. For reference, the first goal is:

100 yards...rest for 12 breaths...repeat 3 times.
50 yards...rest for 8 breaths...repeat 3 times.
25 yards...rest for 4 breaths...repeat 3 times.

Then, once that's comfortable, I'll add in the 200, and so on...I don't really have a distance goal, but I'd like to feel comfortable swimming for about 45-50 minutes - which I suppose will eventually put me at around 1 mile.