Can't use DATEADD(), any alternative methods?

I want to know if there is a way to add minutes to a date. I tried the DATEADD() function but I got nowhere. I'm open to other ways to get to do it.

My code

select 
visits.delivery_max,
visits.delivery_min,
DATE_PART('minute',delivery_max-delivery_min)/2 as diff
DATEADD('minute',DATE_PART('minute',delivery_max-delivery_min)/2 ,visits.delivery_min)

from visits

where 
    visits.delivery_max is not null 
and visits.delivery_min is not null 

Without DATEADD()
image

With DATEADD()

Hi @Vallistruqui
Post "Diagnostic Info" from Admin > Troubleshooting, and which database type you are querying.

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@Vallistruqui dateadd is not a Postgres function:
https://stackoverflow.com/questions/27080505/dateadd-equivalent-in-postgresql
By the way, latest release is 0.39.1

That way did it. Thanks!