A wrong recorder clock doesn't sink your footage: the order and spacing of events are still good. Calibrate each source against one event you can date, then convert any displayed time to the real time, and to what every other source shows at that instant.
Add each camera, DVR channel or device. Calibrate it once: enter a moment it displayed and the real time of that same moment (from a phone record, a receipt, daylight, a witness…). The offset is worked out for you.
Pick a calibrated source and type a time it shows. You get the real time, plus what every other calibrated source shows at that same instant.
No external anchor? If two cameras both caught the same moment (a person crossing between views, a light switching), enter what each one showed. That gives the offset between their clocks.
Elapsed time on one source is reliable even when its clock is wrong. Use it to log "then 26 minutes later…".
Runs entirely in your browser. Nothing is sent anywhere. A helper for building a chronology, not legal advice; for a matter that may go to court, have the reconstruction reviewed by a qualified forensic examiner. Times are treated as plain clock readings (no timezone), so keep every entry in the one timezone.