Three times John uses ἐπαύριον translated 'the next day' or 'the day following'. Then he uses 'the third day'.
Checking the verbs:
- Joh 1:29 John seeth - Present, Active, Indicative
- Joh 1:35 John [had] stood - Pluperfect (once and for all), Active, Indicative
- Joh 1:43 there was - Second Aorist (punctiliar), Middle Deponent (like active), Indicative
- Joh 2:1 The third day
Was the third day the third day or the fourth?
The literal answer isn't as important as the ambiguity which creates the riddle. It suggests that what happened at the wedding in Cana is a parallel to the third day of creation.