Expiration notification 60 days, 30 days, 7 days and when expired workflow for 2013

I have an Asset Registry that we want to notify us when there is only 60 days left on the warranty, 30 days, 7 days and when the warranty has expired. I've seen some examples in SP 2010, but I'm using SP 2013 and I'm not able to figure how to get this to work. We have a column for when the item was purchased and a column for how many months the warranty is for. Then the expiration date is calculated based on those two columns. I also have a column that calculates how many days are left on the warranty. Can I just pause the workflow based on days left and wait for it to get to 60, 30, 7, 0? What if someone extends the warranty at before it expires. What will the workflow do? Will it restart? I'm new to SP and workflow. If some can help me to understand how this works or give me an example I would appreciate it.