There are some major doubts among devotees regarding pradosh vrat. One such doubt is - if I forget the pradosh vrat then can I do on next day?
Yes, the pradosh vrat can be performed the next day. You just need to make sure that you perform all pujas and end the fasting before sunset on the next day.
Trayodasi, Chaturdashi and Amavasya – the three days beginning with Pradosh – are associated with Shiva. So you can observe the vrat on these days to appease Him.
Shiva is Bholenath. He is pleased with any offering that is given with devotion. What is of prime importance is devotion not date and time in vrat related matters.
Know that the ultimate aim of all vrats and rituals is to come out of ignorance and merge in the Supreme Truth.