FD_ALL run 2 task :

• task heartbeat_sender_future to send hearbeat
• task timeout_checker_future to check timestamp of hearbeat received

the thread interval parameter is the same for theses two tasks (FD_ALL.interval)

when you have a long interval, the task timeoutchecker are discovering the loss of a member too late.
the improvement is to decorrelate these two intervals to let timeoutchecker task stick the real member loss