Q. When someone wears Tzitzith, either a Taalith Gadol or Kattan, does he comply with a separate mitzva every second or even a fraction of a second he is wearing it? That would be about 86400 mitzvoth every day! How about if he wears two?

Does the same apply to Tefilin during day time? Does it apply to each Mezuza day and night?
Since Halacha rules that Mitzvot Deuraitah (Biblical Mitzvos written in the Torah) require intention to comply with them does one have to keep his intention and mind to comply with them constantly?

A. Our Rabbonim Shlit’a are of the opinion that as long as one had intention at the beginning of his compliance with the mitzva and that is likely when the brocho was recited, what follows, is accepted as being done withe the same intention.

The above follows the principle of “Kol Haosseh Al Daas Rishono Hu Oisseh” (whoever performs a Mitzva, does it following the initial intention). See Shulchan Aruch (O.H. 60: 4,5 – Mishna Berura 10).
Horav Shlomo Miller’s Shlit’a opinion is similar.

Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller, Horav Chanoch Ehrentreu Shlit’a and Horav Kalman Ochs Shlit’a.