Neither? Both??
But I was able to record mine and it has some sort of pattern in it:
My sleep time tends to move hours to hours ahead of itself.
It's like whether or not my sleep shortens or extends, somewhere along the line I've been disproportionally been awake by at least several minutes or hours more.
So... I'd go from the regular night to day sleep, to sleeping at afternoon then back within 2-4 weeks in cycle.
Something similar to this;
Day 1: 8pm-4am sleep
Day 2: 8pm-6am
Day 3: 10pm-7am
...
Day 7-8: 3am-10am
Day 8: 3:30am-12nn
...
Day 12: 3pm-11pm
Day 13: 4pm-1am
Day 14: 6pm-12md
...
Day 15: (Repeat from day 1 pattern or at least closer to it)
On top of being irregular, there are times my sleep time is fragmented, seperated by hours in between.
Sleep short now, continue later.

It can skip and merge, or just skip entirely and/or merge by itself.
And... Being 'regular' in any way or form seem to never last for few months.
It probably never did maintained the whole year... It'll be disrupted one way or another, sometimes on purpose sometimes not.
Even as a child and teenager with classes, or as a working adult with clear schedules and at least a coherent routine when I should sleep and eat.