I come at the beginning of time, I come at the end of time, I come twice a week and once per year. What am I?

The Letter E!!!

I don't know what it is, but the letter, E, does not come at the beginning of time.

To solve this riddle, we need to break it down and analyze each piece of information provided.

1. "I come at the beginning of time": This suggests that the answer is something that exists or occurs at the very start of something.

2. "I come at the end of time": This indicates that the answer is also connected to the end or conclusion of something.

3. "I come twice a week": This implies that the subject appears or happens on two specific days every week.

4. "I come once per year": This means that the answer appears only once a year, indicating a specific day or event.

Considering these clues, the answer to the riddle is the letter "E."

Explanation:
- The first letter of "time" is "T," and the letter "E" is the first letter of "end."
- The letter "E" appears twice in the word "week."
- The letter "E" also appears once in the word "year."

Therefore, the solution to the riddle is "E," which fits all the given conditions.