Ah, the traveler's friend, Jet Lag.
So, oft the top recommendations go as follows:
Wait Until A "Reasonable" Time To Sleep
Caffeine Is Your Friend
Well, I respectfully offer far different advice.
Go To Bed Early
Water Is Your Friend. Consume Caffeine Only As You Would At Home
Personal experience and those of my travel companions. Having tried both techniques, we vouch for the later.
A 20 minute nap or even 2 hours leaves one refreshed, happy, and headache-free while taking in the new sites. (If you have traveled to a siesta culture, bonus: everyone else is napping anyway!)
Going to bed at 4pm or 6pm the first night may have you up early, yes. Then you can enjoy all the wonders found during the early morn in any given location and be first to the cafe! Likely, you may just wake at your normal wake time.
Extra caffeine may give you a momentary boost, but will undermine your night sleep and may make you as irritable as alert.
Too oft, my friends, family, and I followed the first set of advice only to stumble groggily and grumpily through a town, enjoying little.
Once, the sleep deprivation, aka jet lag, triggered a psychotic episode for one of us. This person has a pre-existing mental health condition and has since traveled extensively and happily by following the second set of advice.
Add an extra day to tour travel if you can to simply rest and reset your travel weary self. Or see the opportunity to nap in a hotel, cabin, homestay, etc as a treat!
It is far better to miss a few hours of dazed touristing and then energetically enjoy the remainder of your time.
Be safe! Be happy! Under the fog of jet lag you are at increased risk for any number of ill events. Losing tickets or money, being pick pocketed, stumbling on that hike, making a disastrous wrong move in that rental car or just having a bad time and creating bad relations with others. While sleep deprived, you are less alert and less happy.
Take a nap! Go to bed early! Drink water!
Travel safe. Travel happy.