I lost my 400W heater on my 110G tank a month or two ago, and the temp dropped from 78F to 68F in the course of about a day. It didn't drop any lower than that, as that's the room temp. It stayed there for about 3 days - the fish were all fine with it. I got a new heater and raised the temp up that way. All's well that ends well.
These fish go through natural temp fluctuation, and having the water cool a little at the beginning of spring is rather normal - ice melt off the mountains above brings cooler water into their rivers and streams. As long as its temporary, they should be fine. Keep an eye on it and if it starts to drop below 65F, then I would add more warm water. If it stays close to 70, they should be just fine.