ssl certificate - renewing with different provider before expiry
If a domain has an ssl cert from one provider that expires for example, on February 17th, and you generate a new certificate from another provider and intall it today (and the certificate has a start date and time 4 hours from now), what occurs -does the old certificate stay in use until Feb 17th and the new ones starts then, or, does the old certificate stay in use until the new certificate starts from its start date and time?