Speculate about time these folk may arrive for dinner (6)
I believe the answer is:
guests
'arrive for dinner' is the definition.
I can't tell whether this defines the answer.
'speculate about time these folk' is the wordplay.
'speculate' becomes 'guess' (guessing is a kind of speculating).
'about' is an insertion indicator.
'time these folk' becomes 't' (I can't justify this - if you can you should believe this answer much more).
'guess' placed around 't' is 'GUESTS'.
'may' acts as a link.
Can you help me to learn more?
(Other definitions for guests that I've seen before include "Invitees or hotel customers" , "Visitors to whom hospitality is extended" , "Folk receiving hospitality" , "They are associated with visiting" , "Hosts entertain them" .)