We do a separate intake session (caregiver interview and unstructured observation of child, often with early intervention staff present as well), with a testing session scheduled 2-4 weeks afterwards. Info from intake is submitted for prior authorization. I deal almost exclusively with Medicaid, and they typically turn around the auth in 2-15 days, but have up to 15 business days, i think. I'll maybe get 1-2 clients a year where no prior-auth is needed, and we still do the intake session.
With my population (toddlers) the unstructured intake- in addition to being necessary for the prior-auth- gives the kiddo a chance to get used to the setting, see that I'm not one of the doctors who gives them shots, etc. It can often take ~15-30 minutes for the initial stranger anxiety and shyness to go away, and that would run too far into the developmentally appropriate attention span for testing. I start the next session with the formal cognitive and language testing. it would be tough to direct the kiddo to transition to the formal tasks after the unstructured free play of the intake interview, so starting with the "boring" stuff first during a different testing session is often the best way to go. As is it, I try to do testing, preliminary scoring, feedback, and written recommendations during the testing session, and that often pushes the kiddos limits! I also can't do much testing after 12, as kiddos are hungry and then we get into nap time (for the clients, not me!). Best case scenario, I write the report same day as the testing.