You should lift the bulbs before the ground freezes, so it could be done anytime now.  Generally speaking, gladiolus can be cured as you would onions and stored dry. To do this, dig bulbs and remove excess soil and foliage. Spread bulbs out in a dry area that has plenty of air circulation, and allow bulbs to cure. After curing, remove dried foliage or excess stems. Dusting with a fungicide is not absolutely necessary but can be done at this time. Store bulbs in a container that allows adequate air circulation (potato sack, paper bag with holes punched in it). Place the container in an area with good air circulation and where the temperature will not drop below freezing.
On the other hand, there is anecdotal evidence that, depending on the micro-climate in your landscape, gladiolus will overwinter in the soil in your area.  You may choose to leave a bulb or two in the soil as an experiment.  If we have an extended period of below freezing temperatures predicted, you may then choose to apply a mulch blanket over the soil in order to keep it from thawing and freezing and heaving and thereby exposing the bulbs.
LS