I've heard the duration of jet lag can be calculated by taking the number of time zones (or the difference in clock time between two points) and multiplying by days, so, for example, Los Angeles vs. London would take 8 days to adjust fully.
Based on that approach, it should take a day to adjust to the time change.
The rest is simply psychological. It gets dark at 5pm instead of 6pm, or gets light at 6am instead of 7am. That annoys people, but there is a simple solution: don't look at the clock. Shift your working hours, meals, and bed time, if possible.