Is anyone aware of any studies done on whether and how soon the "circadian rhythm" adjusts and changes?

Personally, I easily and fully adjust within a few weeks to any new sleep schedule. For 10-14 days, I definitely feel more fatigued and productivity decreases after a drastic schedule change, but things get to normal very soon. I currently sleep at 7am and wake up at 3pm. Just a few months back, I used to sleep at 9pm and wake up at 4am. Previous few years have seen 10am-6pm, 7am-3pm, 2am-10pm, 8pm-4am etc.

As for personal preference, I prefer my 7am-3pm sleep schedule the most simply because nights are more peaceful with no distractions.

tl;dr I have changed my schedules countless times over the years, and after an adjustment period of few weeks, there's little difference in terms of productivity or how I feel.