Timeframe to enter UK for tier 1 visa

I just got my tier 1 visa effective 15th Feb.

Is it mandatory to enter UK within 28 days from the date of visa? What are consequences of not entering within 28 days?

I'll require 3 months to wrap up things here like my current job with a 2 month notice period.

Pls advise.

No it's not mandatory to enter within 28 days, you can enter any time during the time your visa is valid.

If you want to apply for settlement though, entering within 28 days will help towards not having to extend twice (attempted explanation here).