ensure data timer period is suitable with sql time lag

each data is refreshed thank to a dedicated timer, this period is now fixed to 2.5 sec.
it's totally fine when request react fast, usually ~1msec.

But it happen that these requests are much slower, then the timer period is too short, causing the window to more or less freeze. 

This period could be tweaked, a moving average of the last sql latencies multiply by a fixed factor ?