That's basically how porting works. Almost instantly you can start calling out with your ported number, but all incoming is still routed to your old provider's service. When I ported my parents number to PM it took a little over 3 days (2 business days). It was a landline and those usually take far longer than a mobile to mobile port.
The reason why it takes that long is the old provider has to accept the fact you are porting it over and release it. They sometimes drag their heels and make an offer to keep you before ultimately releasing. Also, if it is a landline to mobile, it likely won't be processed on a weekend if the carrier doesn't have that kind of support on weekends.
