Evidently it takes at least 2 weeks to get up and down from Base Camp in order to deal with the altitude. So while there's only 2-6 hours per day of hiking, one has to pace oneself, stay hydrated, climb high, sleep low, and take a rest day or so. So at a minimum, including at least one day either side to get to and from Kathmandu, this will take ~16 days. In actual fact, I'm hoping to include a small side trip that will add another day to the trek. Details to follow when I've got everything booked.
That, of course, was another concern for me but my client have been fantastic and just said to book the general time and when my plans firm up keep them updated. My boss did Kilimanjaro when he was younger so he's behind me all the way.
Phew! Getting time off was my biggest worry.