from time to time
时常，有时，不时
from time to time是 time 的常见短语，是一个表示频度的介词短语，其频度和 at times， sometimes ，now and then是同意表达，都表示“有时”的意思。
from time to time=sometimes=at times=now and then

频度比较
always>usually>often>from time to time>occasionally>seldom>hardly
例句：

1. She sat silently,flinging the odd word into the conversation from time to time.
她静静地坐着听谈话，不时插进一两句。
2. He threw in a word or two from time to time.
他时不时冒出一两句话。