I found short, more frequent, visits really helpful when dad was in the later stages of dementia and in an EMI home. If the visit was going well, I would stay longer, but often I just stayed for 20 minutes or so. Long enough to have some contact, talk to the staff, check everything was ok, but not so long that the visit became difficult or too upsetting. I really think you have to just do what you can cope with and try not to feel guilty.
Blue sea
Blue sea