When its 7 pm PST where is it midnight?

PST is UTC - 8 hours, and 7 PM is midnight - 5 hours, so at 7 PM PST it is midnight in places where the time zone equals UTC - 3 hours. Time zones that equal UTC-3 and that are always in effect are...

Argentina Time (ART) in Argentina

Brasilia Time (BRT) in part of Brazil (The southern parts of Brazil switch to Summer Time from October to February, but about half of the Brasilia time zone stays on standard time all year.)

Falkland Islands Summer Time (FKST) in the Falkland Islands

French Guiana Time (GFT) in French Guiana

Rothera Time (ROTT) at the UK's Rothera Antarctic Science Station on Adelaide Island

Suriname Time (SRT) in Suriname

Time zones that equal UTC-3 and that are in effect during only part of the year are...

Amazon Summer Time (ANST) from the 3rd Sun. of Oct. to the 3rd or 4th Sun. of Feb. (depending on when Carnival falls) in part of Brazil

Atlantic Daylight Saving Time (ADT) from the 2nd Sun. of March to the 1st Sun. of Nov. in Bermuda and parts of Canada and Greenland

Chile Summer Time (CLST) from the day after the 1st Sat. of Sep. to the day before the last Mon. of April in Chile and at the US's Palmer Antarctic Science Station on Anvers Island

Paraguay Summer Time (PYST) from the 1st Sun. of Oct. to the 4th Sun. of March in Paraguay

Pierre & Miquelon Standard Time (PMST) from the 1st Sun. of Nov. to the 2nd Sun. of March on the French islands of Saint-Pierre-et-Miquelon

Uruguay Time (UYT) from the 2nd Sun. of March to the 1st Sun. of Oct. in Uruguay

Western Greenland Time (WGT) from the last Sun. of Oct. to the last Sun. of March in most of Greenland