How are you planning to play these sequences?
From within xLights, outputting E1.31 to your devices? If so, then just create a schedule that plays them back to back for the allotted time.
From a Falcon Pi Player? If so, copy the 6 fseq files to the FPP, create a playlist of Sequences Only, and schedule them.
Unless you are concerned about the slight pause that you'll get as it switches.
I haven't (and don't plan to) tried merging two or more XML files to see it that works. If you are very good with Notepad++, you could try that on some backup copies of your 6 XML files.