Supporting timed buffering

[reborg]

Interesting problem raised by @clumsyjedi. How to support a scheduled buffer like this:

max=10 reqs
0------------15'-------------30'-----------45'
||||          ||||||||||||    |||||||

1. Divide time into windows, like 15' each
2. Collect requests without firing
3. If max=10 reqs reached before 15', fire them (using normal throttling)
4. if max=10 reqs not reached, fire them at the end of the window of 15'