John,
April 20th, 1894 would be the correct date if you are using our current "new system". I mention this because Nicholas's diary entry where he describes their engagement as being April, 8th can otherwise be confused. As Nicholas himself writes...
"8 April. A marvelous, unforgettable day in my life! The day of my engagement to my precious, beloved, Alix. After our conversation we declared ourselves to each other..."
Twelve days later on April 20th Nicholas left Coburg and headed back to Russia.