All aquatic life is used to handling temperature fluctuations during the day. It's just how things work with the sun going up, and back down, every day. Just as long as it's not more than 10 degrees, or very sudden (i.e. putting cold water into an 80-degree tank during water changes) you should be fine.
Tiger shrimp like to be in the mid-70's, but as low as 72 or as high as 82 is fine. Cooler water DOES slow down their breeding as it does with almost any fish, so stick with something closer to 78 for breeding.