Hi,
intervals vary from airline to airline. As LeandroSecundo already stated for what is called simplified C-Check the interval is +/ - 18 month.
see below extract from a A330 maintenance requirement
Code:
CHECK MAX. INTERVAL
MPC
PFC Before each departure
W 14 calendar days
A 800 FH since
C 1C = 18 months
2C = 36 months
4C = 72 months
8C = 144 months
IV 1IV = 6Y = 72 month
D 1D =12Y =120month