But I do not understand anything about timers and my programming level is very basic, I know the existence of the milis but if I use this method I will not be able to use other peripherals later like for example to always be to measure the temperature of the water.
That is complete nonsense. The millis() function only returns the the number of ticks of the clock. Not calling millis() does NOT change the fact that the clock keeps ticking. Getting the number of ticks does NOT affect the number of ticks.
I need to open two valves during a certain time
During? Or for?
if someone can give me some lights, references or some examples ?
I found a youtube video about making a tuna salad. Would that be useful?