This thread makes my head hurt, probably because I'm just looking and am not involved in solving a problem like this.

I have noticed that flag actions take time. I have a pretty simple flag macro on what I laughingly call a "system" in my living room: a TV with toggle only power, a DirecTV DVR, and a Sony DVD player.

When the "system" is on and I turn it off, my T2+ shows the button in action for about a second. This process involves checking the flag and turning off the TV...and there's a clue.

If the system is off and I hit the SYSTEM OFF button, the T2+ shows the button in action for only a couple tenths of a second. And here's where that clue comes in handy: if the flag has been unset, the macro does not execute TV POWER, nor does it unset the flag, and the macro takes less time. I'm sure it takes less time because of no TV POWER command, and maybe also because of no need to unset the flag.

Regardless, if you are using flags, you must be issuing commands dependent upon the state of the flag, so the macro will take a different amount of time depending on whether the state of the flag tells the remote to issue other commands, or not.

As to macros being thread safe, I know my T2+ will not do any next step once one macro has started, until it is finished. I believe that if a macro calls up another macro, that second macro would have to finish before the first one can do the next step. I think it has to be that way, because the remote can't issue multiple commands at the same time and so have to be strictly ordered to work at all.