Jesus ate the meal with His disciples on 14 Nisan (one night earlier than the majority of other Jews would eat the official Passover meal) simply because He would not be alive to eat it the following night. He really did not have a choice to do it at the regular time. Jesus ate the Passover meal with eleven out of twelve of His disciples before being betrayed the following day by judas. 

Matthew 26:17 On the first day of the Festival of Unleavened Bread, the disciples came to Jesus and asked, “Where do you want us to make preparations for you to eat the Passover?”

18 He replied, â€œGo into the city to a certain man and tell him, ‘The Teacher says: My appointed time is near. I am going to celebrate the Passover with my disciples at your house.’” 19 So the disciples did as Jesus had directed them and prepared the Passover.