If the Sky Blues beat Blackburn on Tuesday February 24th at the Ricoh Arena then get a draw against Chelsea on either Saturday or Sunday March 7/8th depending on television requirements in the Sixth Round, the replay will be at Stamford Bridge on Wednesday March 18th.
The playing of this possible game on a Wednesday is due to Chelsea playing Manchester City on the Sunday before in a televised game which kicks off at 1.30pm.
With this in mind, you are advised not to make any travel arrangements for the game at Selhurst Park at the moment.