(feat) Option to dynamically define timeframe

Hello.

Many APIs requires timeframe (from and to fields) in order to get the right response you want. As you might imagine, hardcoding timeframe is not a way to go when i want to check e.g. for bandwidth each 5 minutes.

It would be absolutely awesome to implement some naming like {{now}} and combine it like "{{now}}-15m" to get timerange from 15 minutes ago until the time of calling the API.