For context, not another answer: As @Evert said there is no place for a TimeZone in an iCAL date value, just a year, month and day:

https://www.rfc-editor.org/rfc/rfc2445#section-4.3.4

Formal Definition: The value type is defined by the following
notation:

 date               = date-value

 date-value         = date-fullyear date-month date-mday
 date-fullyear      = 4DIGIT
 date-month         = 2DIGIT        ;01-12
 date-mday          = 2DIGIT        ;01-28, 01-29, 01-30, 01-31
                                    ;based on month/year

...

 Example: The following represents July 14, 1997:

 19970714