Few things to note...
We typically try to use as few template edits as possible to make upgrades easy, just had to throw that out there....
I usually help my clients out for free on minor upgrades if there is something that needs to be fixed, however with the new merge tool it puts more power in your hands to fix outdated templates.
When 1.2 rolled out I helped my past clients as soon as I could, whether it was them sending me their latest XML + style folder and me updating it... or me having an account on their site to quickly do the update live. With 1.2 depending on the style there usually was a charge(small normally) just because of the responsive tweaks involved.
Same thing goes for new clients I will gladly help them with minor updates, however if something major comes up there could potentially be a fee.
In regards to turn around time... it really depends, it's usually best to contact me BEFORE your upgrade so I can arrange a time to help you with that process so you're not sitting on a new version of XF with an outdated style. It also of course depends on my current workload, if I have deadlines to meet for my current in-progress clients my focus needs to be there, but as I said... if you contact me ahead of time I can arrange some free time
Lastly... I was on XenForo answering questions for free for years before I started entering the business side, so any clients who want to upgrade their site by themselves can absolutely use me for a support line
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Sorry if you weren't expecting a novel