Envelopes expiring despite 120 day expiration period

We have a 120 day expiration period on all our envelopes, but one client is saying the link they receive has expired despite it being within the 120 days.

They are the second signer of the envelope before it comes back to us; is this anything to do with it? Is there a certain time period between the first signer completing their section that the second signer has to complete their section or the link will expire?