When instituting the Lord's Supper, Jesus Christ said (Luke 22:20):

> In the same way, after the supper he took the cup, saying, “This cup
> is the new covenant in my blood, which is poured out for you.

 
And in Jeremiah 31 the new covenant is also mentioned, with the blessings of the covenant listed.  Hebrews 8 talks about the new covenant superceding the old in some way (the details of which perhaps I will put in another question). 

**At which stage did this new covenant supersede the older covenant, according to Reformed theology?**