I am building a mobile app and would like to follow best practice for datetime. Initially, we launched it in India and made our server, database and app time to IST.
Now we are launching the app to other countries(timezones), how should I store the datetime? Should the server time be set to UTC and app should display time-based on user's timezone?
What's the best practice to follow in terms of storing date time and exchanging date time format between client and server? Should the client send date time in UTC to the server or in it's own timezone along with locale?
Keep as much in UTC as possible.  Do your timezone conversion at your edges (client display and input processing), but keep anything stored server side in UTC.
Internationalization for datetime