Things like that puzzle me. Why wouldn't a club want to bring a manager in (assuming he is a free agent) as early as possible so he can properly asses the squad and get bedded in before the new season starts without any pressure?
Steve Clark is now favourite ahead of Kennedy. Howe, Benitez and (worryingly) Lampard. 1 is in a role, 1 is at the club anyway and 3 are free agents.
It would be better if Celtic could appoint whoever the new manager will be as soon as possible, but what if he's already in a job and refuses to do a Rodgers and walk out on the club, or country, he's managing at the moment?
One advantage with appointing a new manager in the summer would be that it might create some enthusiasm within the the support, and make more of them renew.
I've noticed Rangers tend to get their signings done pretty early on, while Celtic tend to wait until they find out if they've made the Champions League group stage before they decide who they're signing.