Expecting to render VTT files with timestamps beginning at 01:..., indicating a 1-hour offset, which will be globally nullified so that subtitle text lines get actually shown at at 00:

Hi,
you could correct your subtitles through the Network API the following way :

            conf.network = {
                preprocessHttpResponse: function(type, data) {
                    if (type === bitmovin.player.HttpRequestType.MEDIA_SUBTITLES) {
                        data.body = data.body.replace(/(?<!:)(01)(?=:)/g, "00")
                    }
                    return data;
                }
            }