Alan - many thanks for your reply. I must have been having some sort of senior moment, because it's working fine now!!
However, I have another couple of questions. How would I put the location info on a new line in the tooltip, possibly with the preceding caption "Location:" in bold like the other field titles? I have tried the php \n (newline) character but it seems to be being ignored. At the moment the tooltip is concatenating the location info straight after the time info without a space, which looks awful.
And how can I add the location info to the tooltip for *all* events, not just the multiday ones?
I should be very grateful for any help with these questions.
Kind regards
Andy