Similar to federal student loans, private student loan funds are sent straight to your school around the beginning of the semester. The school applies the money to tuition and other required fees. If there are funds left over, the school will disburse the remainder to you.
Private student loans are subject to laws affecting disbursement dates. Specifically, there is a three-day waiting period after you receive the loan disclosures before the loan can be disbursed. During that time, you can decide to cancel the loan without penalty.