Inconsistent Time Delay

I am using the AD-FMCOMMS5 and attempting to save a series of received signals via MATLAB. I know that the board is constantly transmitting, but when I use the tic and toc MATLAB commands, it appears that the time it takes to begin sending signals is inconsistent. Ideally I would like to start receiving at the exact same time as I begin transmitting, but I cannot seem to do this. I am also trying to step the center frequency to increase my overall bandwidth which might make this difficult.

My received buffers are larger than the transmitted, but the signal begins at varying times in the waveform cycle since the output is not turned on at the exact time the radar begins transmitting. Do you have any suggestions?

Thanks