Latest Image via API Sentinel 2

Hey,

it seems that the time parameter is not set optimally.

If only a single time point is specified, the service will return a mosaic of the images from the beginning until the specified time point (beginning = the earliest time for which the data is available for a selected dataset). This can vary between zoom levels.

If two time points (start and end of the time range) are specified, the service will return a mosaic of the images from that time range.
To get the image of one day, the date (or time) should be set as start and end of the time range (2016-01-01/2016-01-01 or 2016-01-01T00:00:00Z/2016-01-01T23:59:59Z)

More about the time parameter and other WMS parameters available here.

Hope this helps.
Cheers.