[time change and insulin basal: we have been using an insulin pump all along, so this post may not apply directly to MDI users]
For the past three months, we have been traveling non-stop, all summer. We left the US on June 8, arrived in Paris on the same day, left on a long 11-week driving tour the next day. We went South to the Mediterranean, then East to Hungary and Czechia, W and N to very far northern Scotland and the Orkneys, then back South to Portugal and Spain. We arrived in Granada, Spain on Sept 1 and have been there since.
We gained 7 hours from the upper midwest to France the first day, going from longitude 88W to long. 2E. Then, without a change of time, we went all the way to long. 19E, but in many legs. Then we went back to long. 6W (northern Scotland) in 3 long and fast legs, losing an hour. Then we went back to long. 2E in one leg, gaining an hour.
At no time did we see any difference in basal issues. We are experienced travelers, and make sure to get up early and go to bed late the first few days of any longitude change, keeping busy all day, and exposing ourselves to the sun early and late. We saw absolutely so impact on insulin use in any way whatsoever due to longitude changes.
In the same way, we have driven through significants latitude changes, that we expected would impact circadian cycles. In Milwaukee, we were at lat. 43N. From there we went to Paris at 49N, then to the Med at 43N (in one leg), then back up to 59N in the Orkneys and the Outer Hebrides, then back down, pretty fast, all the way to 37N in Spain. We were expecting to see impact as we went up and down in latitude. But we have seen absolutely nothing that we can attribute to latitude changes.
All through summer, we always walked several hours every day (4-8 hours per day) except on driving days, where we would walk less or not at all (we spent several days driving all day long from 5am to midnight or later). We also made sure to get up reasonably early after a driving day, remain busy all day, and go to sleep in the evening.
My conclusion is that, if you remain active throughout the day, expose yourself to the sun as you do that, and follow the local sleeping schedule (i.e. sun-based), large changes of latitude or longitude may not impact your basal insulin use. It did not impact us, in my opinion because of how we were managing our activities and our sleeping schedule. Of course, YDMV 
We did have melatonin but never felt the need to use it.
This post only looks at time change and impact of latitude/longitude changes. Our travel activities resulted in significant impact to basal, and I will cover that in another post.
Note: this is a follow-up from this travel thread:
, so my observations are not as tight or definitive. But it seems that the daily rhythm of my metabolism being slower in the morning and higher in the afternoon/evening doesn’t change time zones quickly, which affects my glucoses. Thus I can have some significant lows if I’m not careful. After 4-6 weeks everything settles down and life resumes a more normal pace. I notice it the most when I travel between the US to PNG - not sure of the latitude and longitude differences, but they are significant. It’s about a 15 hour time zone difference, depending on where in the US we spend most of our time and the time of the year (PNG doesn’t change their time - they are the same as Brisbane). Also, we are below the equator. I’ve also wondered if it’s a simpler problem of my body just being tired - thus easier to miss the signs and symptoms of a low. 
Whatever - I’m grateful that I can do it, grateful for my CGM, and curious to hear other people’s experiences. 