If one does a nirjala fast for Janmastami, highly recommended, then after Sunrise one can take non-grain prasada and then fast from grains till Prabhupada's feast celebration, thus both fasts are observed.
If one has taken non-grain prasada on Janmastami then one can't take prasada again till the Prabhupada feast.
The sastric paran or break fast rules for Janmastami are as follows:
1. After the Janmastami festival (around 12.45) Grains are strictly forbidden.
2. After the astami tithi ending, 3