How to control the flowgraph run and wait?

Hi,

I am tring to write some python script to implement the synchronous
transmit. So I have to control the two flowgraph to decide what is the
proper time to start, and also need some method to wait (for instance,
first send a header then wait some time to send the packet). Is there
some module or method to do this? Any suggestion is welcome.

Dong Li