There seems to be an(other) issue with the marked timespans: it is impossible to combine them if one of them is not recurring but should be only a (Date) occurrence:
In the dev branch of dhtmlxScheduler we’ve added an optional flag that disables the current behavior and allows displaying all defined timespans for the time block.
It’ll be released as a part of the upcoming v6.0 update. If you want to test it sooner - please contact our tech support email, we can send you a dev build
Get a guaranteed answer from DHTMLX technical support team
under the most suitable support plan