It depends on your goals really. If the Masters 45 is your goal doing a race before will leave you fatigued. You will spend bullets in the earlier race. Then doing two races the day before will make you more fatigue for Sunday since you are racing Sunday as well.
For those that I coach I love doubling up in races when you are building for the season. I wouldn’t do it if your big goal was to place well in this weekend in one particular category. But say you were racing for fun and felt you had good fitness have at it! Not sure how many races you do a year or opportunities to race so you might just want to get all you can. Just make sure you properly fuel in the races. Treat it like you will be racing 90 minutes each day. Be ready to have your recovery food right after the first day, stay off the feet as much as possible, and get some good sleep.
Another option I have those I coach do is race one the first day than do two the second day.
Just my thoughts.