Regarding the 100 brachos when does the count start, from sunset or tzeis hakochovim? Night time is very unclear?
In principle, the concept of making 100 blessings a day applies for each distinct day, the day beginning at night, and ending with nightfall the next day.
The question here is whether one can count blessings made in the ‘bein hashmashos’ period between sunset and nightfall, during which there is a doubt over which day the time belongs to.
Because the obligation of making a hundred blessings is not a Torah law, it appears that blessings made in the bein hashmashos period can be counted towards the coming day (this is comparable to other rabbinic laws, such as sefiras ha’omer; the status of making a hundred berachos is not a full rabbinic enactment, and is therefore more lenient than full rabbinic laws).
However, one cannot count a blessing made in this time for both the previous day and the coming day, and the berachah can only be counted for one of the two days.