The SetExpressCheckout API documentation for obtaining TOKENs to attach to requests when calling PayPal APIs states that the default validity period is 3 hours, so it’s good to consider a maximum of 3 hours.

Here’s a partial quote from the PayPal documentation:

By default, the token expires after 3 hours. Contact PayPal customer service to extend the token lifetime to 72 hours.

• Source: SetExpressCheckout Response Message | SetExpressCheckout API Operation (NVP) - PayPal Developer

Incidentally, you can also contact PayPal customer support to extend the TOKEN validity period to a maximum of 72 hours.

That’s all from the Gemba.