Transmitting a waveform, and recording input, at an adjustable rep rate

I'm trying to use GNU Radio to build a test/measurement rig.

At a user-defined interval I want to perform two actions:

 1) Transmit an FM sweep with user definable properties like frequency

 2) And record to a file for a fixed duration.

For the transmitter I was able to adapt the demo case for the lambda function found here: https://wiki.gnuradio.org/index.php/PDU_Lambda.  This seems to work great.

For the recording feature I started with  the example "Pushbutton IQ Recorder with descriptive filenames" (https://wiki.gnuradio.org/index.php?title=Pushbutton_IQ_Recorder_with_descriptive_filenames).  This works by creating a new file, and recording, whenever a user presses and holds a button.  That button sets a variable to true which enables the recording.

But, short of using custom python blocks, I can't figure out a way to trigger the recording at the same time I perform the transmit and I can't figure out a way to stop the recording automatically after a fixed amount of time / samples.