I have noticed from the tables I play on and log. Most of the Roulette Dealers have a time change at 21 - 23 minutes past the hour and 51 - 53 minutes to the hour. Here is a list of some them tables below.
If your using a live dealer try to stop betting before the times stated to avoid a loss you cant get back with that current dealer.
some of the other Roulette tables will change on the hour mark and on the half hour mark. Here are some them tables below that i have played on and logged.
Hope this helps to limit your losses when a dealer change is about to happen. Will keep updating this when i play on the other tables and gather there change patterns.