It is stipulated that only after performing Madhyanikam must paranai be undertaken on alpa Dwadasi days. So, after sunrise, if it is possible to do Sandhyavandanam and Madhyanikam, one must do so and partake food. Even otherwise, only after completing Madhyanikam must one partake food.
If the situation makes one perform Madhyanikam before sunrise, it is also said that Madhyanikam must be done again during the stipulated time.