I would never hold a space more than about 4 months ie the chances of someone else contacting you for this space between now and January are a possibility. I usually encourage parents to wait till they know more about their child's temperament as well as their return to work plans given that there are plenty of daycare spaces in my area but it also means I am not committing that far in advance. I ask them to keep in touch monthly and if the space is still available in January they will be the first family called for an interview. Too much happens in over 6 months to commit on either side.