MobilePush: Set Inbox expiration dynamically to Send Time + 24 hours?

Hi everyone,

I'm working on a MobilePush Journey where customers can enter the Journey at different times. The Push is triggered when a customer arrives at a specific location, and the message should remain visible in the Inbox for 24 hours after the individual Push is sent.

The issue is that under Delivery Options → Send Copy to Inbox, I can only configure a fixed End Date and End Time.

What I need is essentially:

Expiration Date = Push Send Time + 24 hours

For example:

• Customer A receives the Push at 10:00 → expires the next day at 10:00
• Customer B receives the Push at 18:30 → expires the next day at 18:30

Since contacts enter the Journey at different times, a fixed End Date/Time doesn't work for this use case.

I also have an expirationDate custom key under Advanced Options → Add Custom Functionality. I tried calculating the value dynamically with AMPscript:

%%=FormatDate(DateAdd(Now(),1,"D"),"yyyy-MM-ddTHH:mm:ss")=%% 

However, I haven't been able to get this approach working.

Is there a supported way in MobilePush / Journey Builder to set the Inbox expiration dynamically to Send Time + 24 hours for each contact?

Alternatively, can the expirationDate custom key be dynamically populated based on the actual Push send time?

Thanks!