Here is my recommendation.
Do NOT go crazy in the first minute. This will flood the legs with lactic acid quickly and make it difficult to hold power for 20 minutes. Rather, ease into the effort during the first minute. For example.
If your current FTP is 200 and want to target 210, I recommend starting at 210. During the first minute slowly increase the effort from 210 to 221 watts. For the next 9 minutes ride at 221. This should be doable if you are looking for a 10w increase. Assess the situation after 10 minutes. At this point, you will be slightly below your target because of the 1-minute ramp. If you are feeling good, increase the power slightly for the next 5 minutes. Maybe increase 5 or 10 watts. If you are not feeling good, hold at 221. After 15 minutes it’s all about eating the pain. You just need to overcome the pain and hang on for dear life. Try like hell to hold the 221 and tell your legs to clear the acid. I actually talk to myself and say, “clear the pain”. I’ve been practicing that and it actually works.
If you’ve only done two tests, these should be a positive and exciting experience. Have fun and enjoy the growth!