Used to change the subject or add a related remark in conversation or writing. Often appears at the beginning of a sentence.
By the way, what happened with that matter?
sometimes; occasionally; on occasion
Adverbial use meaning 'at times' or 'now and then'. Can appear mid-sentence or at the beginning.
By the way, what time does next week's meeting start?
He is sometimes late.
He sometimes says harsh things.
Just then, a big earthquake struck.
ところで is the more common everyday word for changing the topic, whereas 時に sounds a bit more literary or old-fashioned in this use.
時々 is the plain, common word for 'sometimes/often', while 時に in this sense feels more literary and slightly less frequent-sounding.
all at once; at the same time; simultaneously
From 時 (とき, 'time') + に (particle). The conjunction and adverbial uses developed from the literal meaning 'at the time'.