Hello René,
The LV User manual gives some help. Use "Timed Loop (FPGA Module)" as the search term in the help and select topic 7, which has to same title.
The talk about a single timed loop.
The single timed loop can contain the function "Set occurrence". Your loops can be synchronised by waiting for that occurrence in all the loops that you want to synchronise.
I hope this help,
Kind regads,
André Buurman @ CARYA
Regards,
André (CLA, CLED)