I think she means "the less treatment-resistant the participants are, the longer the treatment remains effective" (not that the session drags on longer).

The results of this study are pretty exciting, but the idea of using various forms of TMS to treat depression has been kicking around for a while, and several groups have been trying to optimize the stimulation in different ways.

Here's a decent review of its effectiveness https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6582998/

and here's another group that's trying something similar: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5344760/