There is a consensus to 10-20 minutes, and I set the limit to about 10-20 minutes too. But before I start a spell or calling the quarters, I lightly meditate for as long as I feel is needed, depending on what I’m returning from to that point. If it is a bustling day, dealing with others negativity, spend more time meditating, but before I even start, get myself in the mood (even the day before I try to keep my mood and self in order). Then I start with the spell, and at some point, usually after saying the last verse I meditate for 20 minutes, it was good enough for me. Spells that require the burning of candles straight through. I will choose a 4-5 hour burning candle. Still after 20 minutes of meditating, I sit with the candle until it burns, but I’m not meditating for the whole time, still keep it at the 20 minute mark. Before I start, I bring some spiritual, craft, personal development type books/material, if I have paper work - try not to do this too much - but sometimes need to follow up - so I bring that in as well, or my journals to work, organize, but ultimately my time with the candle, keep my activities near it and for that time high energy (edit:sometimes I take a nap too). That’s for the initial spell, but if I have to carry it through on other times. For the other times, I go through the spell, mediate on it for 10-20 minutes, and just let the candle run on its own. The motions have already been set.