Timing a flowgraph execution

Hello all,

I would like to set a timer to create a percent complete graph with
the "QT GUI Level Gauge" block. I've created a flowgraph that does
this and attached a screenshot and the flowgraph. My goal is to have
this kind of "percent complete timer" to tell me when to move my
antenna during a satellite pass. This means adding a piece of
hardware and its connections to the attached flowgraph and I am
worried about having two timers in the same flowgraph.

If I use this flowgraph and add hardware and use a head block with
"samp_rate * duration" items it doesn't complete at the same time as
the "percent complete timer". There are more items to complete for
the hardware when the "percent complete timer" ends.

I have tried to use the "Function Probe" block to probe the source of
my hardware piece, but that doesn't work properly as the timing is off
for both timers.

Does anyone have a suggestion on how to calculate the percentage
complete from the timer on the hardware piece instead of using a
separate null sink as I have in the attached flowgraph?

Thanks in advance,

Chris