If I re-format your text like this, it makes more sense - stream-of-consciousness prose is very hard to understand, especially for techincal matters.
and as you suggested i think it is best to keep the master as listener and slaves to send only when data has to be send
there is no need for setting specific time interval for sending data as it
willwould have to wake up a slave for sending data at a specific time,instead of that only to send data when there is an occurring of an event.
That seems to suggest you are planning to have each slave send data whenever there is new data to send.
And if that is correct I don't understand why you are asking the question in your final paragraph. Why are you thinking it might be necessary to open a pipe for a time period? Why wouldn't the master be listening all the time?
...R