If multiple markets are refreshed at the same time in the fastest mode, then, depending on your PC performance and the refresh rate you've set for these markets, some refreshes may be skipped. E.g. you've set 10 markets to refresh at 0.5 sec, but this is too much information to process, so Time Machine will be able to manage a refresh at every 2 sec. But, like I said, this depends on the characteristics of your system.
Other than that, there are no restrictions or alterations to the way the markets are refreshed and triggers performed.