Dry hopping in secondary (carboy). How long is too long? I usually only go a few weeks before bottleing, but haven't been able bottle the batch due to traveling.
Every hop is different. In some cases I have had grassy flavors from the hops quickly and other times I can leave them in my kegs for 2 months with no issues.
If you can get the carboy chilled you will slow down the process and give yourself more time if you are worried about grassy or off flavors. You could also rack it into another carboy for extended bulk aging.