Depends... Since its 1 h/CL after concentration, and each hour has 600 rounds, and if the BBEG disbelieves all of them, and its encountered in the very last round of the duration (before the first one expires), then thats
(max)600 Perilous Veils / CL x 5d6 per succeeding = 3000d6 / CL
A ridiculous scenario, for sure... If we assume CL 16 (the earliest one could take it) then that becomes
(max)48000d6 ~ 168000 (its over nine thousssaaaannnndddd!!!!)
If we assume the BBEG has really low Will saves, and you maxed your Cha (b/c you wanted to survive at lower level), and the BBEG has to roll a 20 to disbelieve, then the average would be
2400d6 ~ 8400 damage
So, between 8400 and 168000 damage as soon as one gets it. Don't show your DMs... DFAs are already (incorrectly) considered overpowered by many.
Would simulacra help in this cheese?