Sehri and Iftaar

Fasting without sehri

Q: My question is a night before Rajab (miraaj un nabi) I made intention of fasting keeping roza. I stayed up a little with some ibaadat so I thought I will take a hours rest an then get up for sehri but I didn't realise I fell asleep and woke up next morning. Can you please tell me if I am gunaghaar an will my fast be accepted? Can I carry on fasting during the day or not?

Changing one's niyyat before the fast commences

Q: I made a niyyat for a nafil fast about 30min before sehri ends. Just prior to sehri ending, I decided that I should rather wait and make the niyyat for keeping fast before half the day, depending on how I felt. I was not going to eat during that time, until my niyyat was confirmed. Is it ok to change my niyyat for fasting afterwards, or is the first niyyat I made 30 minutes before sehri ended binding?