You can use the current Quicktime to trim the front and back of your clips and then re-save the trimmed clip. I'm pretty sure time and date from a GoPro will remain intact. I think Quicktime 7 (the old version) allows you to trim any section within the clip and splice the sections together.
Creating history....one edit at a time !
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Trim Clip - Keep Date & Time
01 May 2019 12:24 #99866