Is the difference between and saying 有时 and 会偶尔 very big? Does one imply a much greater frequency? What about register? Is the difference between and saying 有时 and 会偶尔 very big, or is it in all cases quite close?
To me, 有时 and 偶尔 are interchangeable under ANY circumstances.

Depending on personal preference, feel free to pick either one when expressing once in a while.