Adam Clarke on John 6:4

And the passover - was nigh - This happened about ten or twelve days before the third passover which Christ celebrated after his baptism. Calmet. For a particular account of our Lord's four passovers see the note on Joh 2:13.

For thirty days before the Passover there were great preparations made by the Jews, but especially in the last nineteen days, in order to celebrate the feast with due solemnity. Lightfoot supposes that what is here related happened within the last fifteen days. See Calmet's opinion above.