Both forex and cryptocurrencies use UTC timezone by default.
Equities and others
All other instrument types, such as equities, ETFs, indices, etc. - use the exchange's timezone. See the below table for an idea:
AAPL, SPX, QQQ
Eastern Standard Time (ET)
India Standard Time (IST)
Greenwich Mean Time (GMT)
How to change the timezone?
Endpoints that contain datetime field in response can be converted into the timezone that matched your use case. The modification is done via &timezone parameter and full documentation can be seen by clicking the Advanced button in the documentation.
For instance, to get Apple Inc time series data in Central European Time (CET), use the following query: