If you notice that quenching
the reaction is exothermic, cool the flask with an ice bath.
Quench only when your TLC or other
analysis method indicates that the reaction is complete.
Beginning students often simply trust the literature time period,
and never check their expereiment. Experimentals in the literature
do not always give accurate reaction times, and if your compound is
slightly different, it will react at a different rate.
Remember that quenching with aqueous solution at low temperature
will result in formation of ice--so don't panic when precipitate forms.
Let the reaction warm up (and the ice melt) before continuing with the workup.
If possible, work up the reaction immediately after quenching it.