Just translate 要是 into "if", the other character "就" is needless to translate. That's to say,
要是......就=If.......,........ or
要是......就=........., if..........
你要是有时候(should be 有时间),就来我家玩。If you have time, come to visit my family.
Drop over to my house, if you have time.
要是明天不上课,我们就去上海公园。We will go to Shanghai Park, if there is no school tomorrow.