How can we introduce network latency to a link?

Apps dev team has requested we introduce 50ms latency to two of their lab switches so they can test stuff across a simulated “high latency wan link.”

I thought I could do that with the delay command, but it’s not actually working.

I set the interface delay command on both sides of the link even to the maximum value, but latency to their lab switch is still <1ms.

Any ideas?