This depends on where you live and the climate/temperature there. For example, in the UK, you can prep it almost any time of the year as it doesn't often get humid OR too hot (I type in the middle of a heatwave -sigh). However, in general, I prefer making miso in the cooler months (fall/winter). The air is usually less humid and contains fewer contaminants; the colder weather also helps it ferment slower for a deeper, more developed flavor. Just note that the temperature can impact the fermentation speed of this miso paste recipe. When prepared during warmer months, it may only take 3-4 months to reach your desired flavor. If this is your first time making homemade miso paste, I recommend testing the miso around the 3-4-month mark, continuing to ferment until it reaches your desired flavor.