How long does swelling/bruising usually last after dissolving lip fillers?

This is absurd advice. You are naturally going to be beaten up from your service. It generally takes several days for the trauma to settle down. This may be minimal or it might be more dramatic if you bruise. Plan accordingly.

Swelling and bruising are not uncommon after lip injections and can take up to two weeks to fully resolve. You can help minimize these effects by avoiding aspirin, vitamin E, fish oil supplements, and NSAIDs a week prior to treatment. The supplements Bromelain and Arnica are also helpful to some patients. Keep your head slightly elevated and use cold compresses after treatment. Ask your injector to apply ice prior to treatment as well.

Hi Mrs Mary,Bruising is an expected side effect after any procedure involving a Needle, but it's Not a must.
You can minimize the risk by applying cold compresses immediately before and after the procedure and you can use Anti-Bruises creams, containing Arnica Extracts. It's really effective.
The Swelling depends mainly on the amount used from the dissolving agent.
Your doctor might prescribe a short-term oral steroid medication if you're highly concerned with the swelling, otherwise let it go Naturally.