Thats an issue with the time library, not with timestamps. Actually timestamps are always in UTC, you need to do the conversion to your local time when displaying the value. There should be no possible off-by-one errors, unless you are doing something really wrong.

“Improve performance by removing a function that never did anything” the story of my life

Kotlin without a doubt.

Gives you more flexibility and freedom that most scripting languages. The syntax is clean and concise, the tooling is amazing and can compile to JVM, JS, Native and WASM.