autopilotNOR:
If I need now to send this updated value more often then, for example, every 10 second like every 3 seconds the problem is that I do not have accurate enough measurements from the flow sensor.
The only data you have is the most recent pulse from the sensor. You cannot assume that there will another pulse ever, or at any particular future moment.
You can calculate the flow rate based on the most recent pulse (or an average of the N most recent pulses) and you can repeat that value as frequently as you want. But it make no sense at all to anticipate the next pulse.
...R