Your dependent care FSA may also consider a change in daycare expense as a qualifying event for dependent care FSA open enrollment.
In our case we had family cover daycare (Free!!!) for the first few months after our daughter was born, then moved on to a formal daycare. Usually this is not an enrollment event, however going from free daycare to paid daycare opened up the dependent care FSA enrollment because the cost of care changed. This means changing daycare, enrolling in daycare, or a change in rates could all allow for enrollment, no need to decide now.
This seems to vary by employer, so I would check first.