I always allow for 3-5 days of vacancy because I need time to properly inspect, arrange for cleaning and repairs, etc. I used to try back-to-back tenancies but it resulted in too many problems when a tenant wouldn't leave it clean, wouldn't move out on time, etc.
I'm not sure I understand the question, but as long as you give the current tenant the legally required length of notice for the non-renewal of the lease, after they move out, someone else can move in immediately.
Edit: if it's clean and move-in ready
Yes that is what I’m asking. Do you make a tenants lease for say July 1, 2018-June 31, 2019? Then the next tenant Lease starts July 1, 2019. I just wanted to see how you make it so you don’t have a full month without a tenant...if possible.