UserAPI.h says that GetTimer returns an unsigned long.
EasyCv2 Variable type help reports that an unsigned long is 0 …4 Gig
Naturally, any variable used to store the value of GetTimer should also be declared as type unsigned long.
When using PrinttoScreen, use format %ld to print the value of GetTimer correctly, otherwise it will show up as int(n/64k) or appear to rollover at 64k when typecast with (int).