A blue area of any colour designates an area that can contain the bio. It doesn't tell you exactly where; for that you need to read the codex or simply have experience tell you where each grows.
Personally, I cycle through the filter after scanning, find the smallest areas of blue and fly to the edge of that area. I keep a note of a heading that I know will take me into a second area of larger bio signals; I fly around and land close to bio's without bothering with the SRV and usually find what I'm looking for pretty quickly. Experience tells me Discus grows on rocky edges, but there is probably Fungoida on flatter areas close by and others at the bottom of the ravines. That's 2 or 3. Then with the heading I took before landing, I will fly a few kilometres in that direction until the ground changes, say from rocky to sandy, in which case I know I'm in a different area for different bio's. Going from rocky ravines to flat sand probably means Stratum, Tussock, and Bacteria etc.
Rarely do I need to fly into orbit and down again to complete. You can usually complete all scans by entering just 2 different neighboring areas in my experience, at least in the bubble. Go to the Borfor system, planets 1C and 1D. Shoribelu 5B 5C and 9E as well. IIRC some of them have 8? 9? signals each, should give you plenty of experience for the most common bio's to find. Make a note of where you found each type growing (side of ridges, flat open areas, inside craters or ravines, sandy, rocky, high up or low down etc).
Yes it takes time to learn, but you should eventually get to a point where experience will help you quickly assess where likely areas within a blue area for each bio are. If it takes too long after that, just move on; the money to time ratio isn't worth completing it. Don't feel like you have to rely on the SRV either; nothing wrong with just landing in the ship and disembarking and you are likely to cover the distance required for diversity between the 3 quicker and more definitively than in the SRV.
Again, all of this is just my experience in the bubble, but I've been completing entire 5 signal planets in under an hour and 9 signals in about 1h 30m. But only after knowing where things grow. I should also point out I'm a VR player which makes looking for bio's from the cockpit very easy.
