Imaginary Coherency Output - Time Average

my time is being listed as [-1.0, 143] s and it states 'Time average' below it. Does this mean the coherence values being displayed are averaged between these two times? When trying to use the arrows to change the time, i can only go to these two values, nothing else. Why is that?

It indicates that in the options of the process "Coherence 1xN", you selected the option "Concatenate input files before processing". This created a long file with all your epochs concatenated. Then the coherence was estimated over this long time window. In output, you get only one value, and the time bounds are kept just to indicate how long was the segment of data in input.
After concatenation, the cross-spectra of the signals are estimated by blocks, similarly to what is done for the PSD (https://neuroimage.usc.edu/brainstorm/Tutorials/ArtifactsFilter#Evaluation_of_the_noise_level). I guess this is not what you expected to obtain...

How can I get greater time resolution so I can look at how the topoplot changes over time?

You can use the process "Time-resolved coherence". This would estimate the coherence by short blocks in your epochs. But 2s seconds is very short to split it in many smaller time windows. Just like it is explained for the PSD, you need many windows of at least 500ms-1s to estimate a proper spectrum.

For more information on how the coherence is estimated in Brainstorm, please refer directly to the comments in the code: brainstorm3/toolbox/connectivity/bst_cohn.m at master · brainstorm-tools/brainstorm3 · GitHub
We are still waiting for new tutorials and test datasets to explain properly all these things.

I was hoping to have a sort of coherency map for each electrode, showing the evolution of the coherency for each frequency over time to compare with my results from FieldTrip. How can I get such a map if possible?

I'm not sure what you did in FieldTrip, but it might not translate to this process "Coherence 1xN" you used in Brainstorm. This will not give you any fine temporal evolution. Maybe something like "coherence before TMS pulse" vs "coherence after TMS pulse", but not more refined than this.
Can you post screen captures of what you obtained with FieldTrip? together with the names of the functions and main options you used?

If you are expecting to compare "coherence before" vs. "coherence after", maybe you could run the process Coherence 1xN twice (once for the 1st second, once for the 2nd second), using the option "Save individual results", and then run a non-parametric test to compare across trials what the differences are before and after the TMS pulse?

@Sylvain @hossein27en Any suggestion?