When I send an specific date picker property update converted in UnixTimeMilliseconds, HubSpot shown the date with one day less. I don't know what's the cause of this.
I tried different methods to convert the date to UnixTimeMilliseconds. I also included the UTC just in case, but the problem continues. Sometime the date is including correctly and other time is including with one day less.
This is an example the method that I use to convert the date:
DateTimeOffset.Parse(mydate.FromUTC("Central Standard Time").ToString()).ToUnixTimeMilliseconds().ToString()