Please keep in mind that discount rule activation time depends on quantity of products. Also only one discount rule can be in process at one time - the rest will be in pending status.
The velocity of discount rule activation (or deactivation) is about 2 products per second, i.e. it takes 5 seconds to apply a discount to 10 products.
In addition, each discount rule may be waiting for the process to start up to 1 minute (pending status).
Discount rule activation or deactivation progress can be tracked near the status badge.