The European Tour (DP World Tour) has introduced a secondary cut, better known to PGA Tour fans as Rule 78 or the MDF Rule, starting with the 2017 BMW International Open in Munich, Germany.
The European Tour's third-round cut rule is very similar in nature to that of the PGA Tour, which has since been eliminated. If 78 or more players make the 36-hole or second-round cut in a tournament, then there will be a secondary cut after the third round. On the PGA Tour, that cut is made to the number "nearest 70 as possible," while on the European Tour, that number will be the top 72 professionals and any players tied for 72nd place after three rounds.
Amateurs will not count toward either the second- or third-round cut numbers. They're through regardless since they don't earn money or Race to Dubai points (which are basically the same thing).
The 54-hole cut won't be made in situations where the field has to finish the third and fourth rounds on a single day.
At the 2017 BMW International Open, 83 players made the 36-hole cut, requiring the European Tour to have 42 tee times on Saturday as they played in twosomes. While players were cut after the third round, all will be paid this weekend.