Hello, I submitted an update and new illustration for my existing font, does anyone know how long it usually takes for the update to take effect? Thanks!

You can add an illustration yourself. Go to My Account -> click the update link next to the font name, and follow the instructions. Submitting a revised version of a font already posted is handled by staff, and is probably a lower priority than approving new submissions.

Some years ago, when there was a short period of time between when a font was submitted and when it was posted, certain font authors used to intentionally submit fonts that were not in their final state, then they would submit a series of updates, so that their work would constantly appear on on near the first page of new fonts, and their download stats would be inflated whenever someone downloaded the newer version of a font they already had.