Most likely, yes, one needs aprox 9 GCDs to get to the 80 Ninki with Mug.

Its killing me the unknown factor of what happens with TenCJ if Mudras are on CD tho...
Because if TenCJ enables 3 Ninjutsus even if its on CD, it means 5 Jutsus in a row... Natural + Kassatsu + 3 TenCJ
But if it doesn't...