Hi @Aleksandra Kurysheva
Without the derived properties feature ( part of Govern Add-on ), it won’t be easy to split and truncate the user property value to display just the date part.
When you create a new user property, Amplitude will expect you to send that new property with events and move it from the planned phase.
So in absence of derived props, you will have instrument the date property as a new user property.
For your 2nd use case, you’ll again need derived props for calculation using the available date functions as shown in this post
Afaik, there isn’t much that can be done in absence of derived props apart from sending the desired calculations as additional custom user properties.
If your secondary use case is aggregating a set of users who joined between certain dates as isolated segments, then using either glob match / contains or <,> operators on your date time property will help to some extent.
Hope this helps.