Timezones are originally designed for adjusting the clock to 12:00 noon when the Sun it at its highest point. In the 19th century many towns had their own timezone. Later it became standardized to divide the world in 24 timezones so that it is noon at 'around' 12:00 o'clock. It is designed in a world without internet, instant communications and intercontinental travel in less than a day.
And then daylight 'saving' time (I rather call this 'daylight shift time') got invented to get longer daylight (at the expense of shorter daylight / longer darkness in the morning).
The 24 timezones still exist, but very messy. some countries tend to shift the timezone to get noon ar 13:00-14:00 hours, sometimes year round. And countries (e.g. India) with half hour offsets. And the DST start and end dates are getting more and more randomized, the EU and US have the best standization.
The excellent site
www.timeanddate.com tells in a very nice way how it works.
In aviation this is very confusing. On Flightradar24.com one can select UTC times which is a relief.
I know it will never happen as mankind prefers to stick to the figures the clock points to and thus does not like a date switch in the middle of a business day (although night shift workers do change date on their 'business' / work day).
But I'd think, the best thing is switching to a worldwide single timezone (can be UTC or any other timezone), just like the whole world (except a few countries which comprise < 5% of the world population) uses the SI/metric, use 220-230V AC mains voltage, use feet (the only non-SI use) for flight levels.
Then the so-called 'international date line' becomes obsolete, all times in aviation are unambiguous. In this era with an internet connected world, handheld devices which will tell you, even offline, what the solar time is anywhere in the world, different time zones are something of the past.