Dear Octavian,
Indeed, the epileptogenicity process was not capable of processing negative time values.
I tried to fix this issue in this commit: https://github.com/brainstorm-tools/brainstorm3/commit/cee9839baa79644522c0f123f917551176615a2d
Update Brainstorm to get this fix. There might be additional issues related with these negative time points in the ImaGIN_* functions, be careful.
Thank you for reporting this problem and suggesting a solution.
Francois