Ideas for clocks web app

Since I often need to know what time it is in different cities in the world for work, I’m thinking about writing a simple web app to show me the different times.

Here are the specs:

• clean and simple
• mobile friendly and accessible offline
• it should take Daylight Saving Time into account
• it should be possible to give a name to the clocks (apart from the city)
• autocomplete to add a new city/clock (with actual cities)

Optional

• set a specific time and know what is equivalent in other cities
• manually sort the clocks

Useful resources

• free cities API
• city details (doesn’t provide DST details)
• Google Maps API to get DST details