Data taken at - Level 1, Garden 3 (Fertility - Low), Unwatered, Unmulched

Gardens 1 & 2 (Fertility - Medium) halve the time. Haven't tested Garden 4.

Watering seems to reduce the time by 20%.

Green 🟢 - "Fast"
10 minutes - Cheri, Chesto, Pecha

20 minutes - Aguav, Aspear, Bluk, Figy, Grepa, Hondew, Iapapa, Kelpsy, Leppa, Lum, Mago, Nanab, Oran, Persim, Pinap, Pomeg, Qualot, Rawst, Razz, Sitrus, Tamato, Wepear, Wiki

Blue 🔵 - "Medium"
1 hour - Belue, Cornn, Durin, Magost, Nomel, Pamtre, Rabuta, Spelon, Watmel

2 hours - Babiri, Charti, Chople, Coba, Colbur, Haban, Kasib, Kebia, Occa, Passho, Payapa, Shuca, Tanga, Wacan, Yache

Purple 🟣 - "Slow"
6 hours - Apicot, Chilan, Ganlon, Lansat, Liechi, Petaya, Salac, Starf

Red 🔴 - "Very Slow"
20 hours - Custap, Enigma, Jaboca, Micle, Rowap

Approximate graph of level (x) by time (y) [Garden 1/2, Cheri/Chesto/Pecha berries, Unwatered/Unmulched]: