"Initial date value" different from the one entered

Problem/Motivation

Upon opening the "Calculate a relative date" action for editing, the value of the "Initial date value" is different from the one that was entered originally.
For example, if the original value was "1970-01-01 00:00:01" after opening for editing, the value is "1969-12-31 23:00:01"

Steps to reproduce

Add the action into an empty rule and set the "Initial date value" field value to something like "1970-01-01 00:00:01". Then close and reopen the action - a value is in that field that is different from the originally entered one.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes