My advice, as in most things tea-related, would be to let your tongue
be your guide!

Many teas are unaffected by being left in the air for a few hours,
while some (particularly the more "green" teas: baicha, lucha,
qingxiang wulong) tend to turn a bit "brown" in flavour if left to
sit. If you are planning to pause for a while, you might like to
ensure that the leaves are kept in a closed gaiwan or pot - the onset
of "brown" flavour seems faster without a lid (perhaps due to the
increased ventilation).

Leaving pu'er overnight (in a closed vessel) is a fairly normal habit
for me, particularly for the occassional rarer pu'er that I really
want to get the best out of, including another day's brewing. Also, I
have come across a few pu'er that actually tasted much better the
morning after, oddly enough, in which previously-absent vanilla tones
appeared from nowhere. Perhaps placed there by the pu'er fairy.


Toodlepip,

Hobbes