On a sunny day go out into your yard at 8 A.M., 10 A.M., 12 P.M., 2 P.M. and 4 P.M. and take notes on the parts of your yard that are getting direct sun.  If the sun is hitting your proposed garden spots, jot down the estimated amount of time the direct sun is on the garden bed during those time frames. You don't need continuous sun for 4-8 hours on a specific bed. It can be additive. You just need to accurately total the amount of direct sun that falls on your garden beds over the day. You can watch this video below for full details on how to do this.