What Date and DateTime does kernel use for valid time state tables

I had to check whether a record in valid time state table is valid now and I got curious about what Date and DateTime values are actually used by kernel.  The answer seemed to be obvious, but in fact it was not. Please find the details below.

Problem description
There are several cases when kernel generates values for valid time state tables:
- ValidFrom field default value set by kernel when a new record is created
- ValidFrom and ValidTo ranges added by kernel into a select statement.
Let's analyse them.

Questions to analyse
1. Is session date and time used?
2. Is client machine date and time used?
3. Is user time zone used?

Hints
Create two valid time state tables with ValidTimeStateFieldType property set to Date and UtcDateTime. Try to change session date and time, client machine date and time, user time zone and compare default values of new record in different cases.