Time Aware NDVI

You can use the Sentinel Hub WMS service to return NDVI products in a GIS software or other application. Here are a few links to get you started:

• information about the WMS API: WMS
• integration with GIS software: QGIS and ArcGIS
• a youtube video dedicated to WMS in QGIS: WMS in QGIS

Also was there a Legend for the NDVI service?

There is no automatic legend for the WMS service, but you should be able to build one quite easily.

And lastly is it possible to query the pixel values?

Absolutely, rather than return a 3-band RGB combination to represent your NDVI values with colors, you can directly return the values themselves. This is done by setting your custom script. Furthermore, a webinar was released last year on writing Custom Scripts.