A frequent recommendation (e.g., here and here) for retagging or otherwise editing multiple questions is to do it when traffic is slow. Then edit-bumped posts will only push older questions off the first page. However, I have zero intuition of when traffic at CrossValidated is slow, or when it is busy.
When is traffic slow or busy around here?
(I'd assume that this is also relevant for other SE sites and was tempted to ask at Meta, but I guess answers will differ between sites, and I don't know whether to expect a simple query that one could customize for different sites as an answer to the "general" question.)