The time length of volatile out-gassing is completely dependent on a wide range of factors. When considering whether or not to use something within vacuum applications you must first use the "smell" test, if you can whaff vapors from a compound towards your nose at atmospheric pressure and detect a scent, chances are that this is not a good candidate for use in a vacuum environment. Outgassing rate is product of the epoxy's constituents vapor pressure, chamber temperature and ultimate vacuum pressure attained. NASA compiles a list of epoxy/adhesive/lubricant suitability for vacuum use which can be found in the following link:
http://outgassing.nasa.gov/
Depending on the epoxy you selected it could be a day or two or continue indefinitely, especially under exposure to plasma due to its vicinity to the inner grid. Hope this sheds some light on your question. Had you considered using alumina stalk to avoid the use of the epoxy altogether or minimize its use?
