The DPDD specifies that during Alert Production, the positions of previously-identified DIAObjects will be force photometered and the results added to DIAForcedSource, similar to how images taken before discovery of a DIAObject are force photometered in precovery.
There does not appear to be a document stating how long this photometry must continue. Clearly we don't want to photometer a point of sky for the duration of the survey if it was a false positive that never reappeared. Eric Bellm and I both remember 12 months as the duration after the last appearance of a DIASource that force photometry continues, but can't find any documents supporting this. LSE-81 and the sizing model assumes that force photometry continues for 1 month. The DMSR specifies that the precoveryWindow is 30 days, though no mention is made of this "post" discovery photometry.