I keep trying to throw a party but all of the guests say they have to leave 10 minutes after they show up. Any tips?

The Legendary Host lifetime reward also does wonders. Use cheats/mods to get the LTH needed for it, if you must.

If this were me in real life, I would seriously consider spending more time on my personal hygiene before the party takes place. And possibly tidy the place up a bit. You know, drastic situations call for drastic measures.

If you don't want an orchestrated feeding frenzy quite so close to the guests' arrivals (though that will work too if your food doesn't make them all sick), another approach is to be sure someone is stationed by or near the door or wherever the guests are gravitating to upon arrival -- usually they will try to head for the one who arranged for the party -- and engage each of them in conversation. Compliment them, Brighten Their Day, whatever you have to work with depending on your sims' traits and theirs. Bring them a drink or a coffee if you have those available. Give them something to do. Suggest they chat or dance ("Convice To") with someone. Start up a time consuming 4-person activity like a video game, table tennis, shoot some pool, have a game of dominoes. Pull them by the hair and drag them into a hot tub. That kind of gracious host thing.

And if you don't have much to work with on your home lot due to its size or lack of funds, consider throwing a party on a commercial lot where there might be more fun things to hold their interest for longer.

Someone mentioned that they use one of the NRAAS mods to give the people they wanted to invite the day off from work. Anyone try that before? How would that work, igazor?

Make sure at least one sim dies. According to several simmers' testimonies, that makes every party a hit.

I do that sometimes. The process is really to add one to their accumulated number of days off (most of them won't have any to begin with). But if party day was not a workday for them, they will get the next workday off instead. Or you could look up each of the guests' schedules individually if you don't already know them.

On the sim, or City Hall if you want to choose the sims from a list,

NRaas > MC > (Sim) > Status > Career (to see their work schedule)
NRaas > MC > (Sim) > Intermediate > Career > Days Off
(MC Cheats add-on module required)

I kind of wished sims attending parties would have a stay-here override that would make them stay for at least half-an hour.

Looking at the XML for House parties, guests should stay a minimum of 2 hours before they leave, barring a very bad mood.

The game also seems to check every 15 minutes in game for a chance that guests will leave the party. Maybe changing this to 30 or 60 or even 120, would ensure that sims stay longer before having a chance to leave, if they don't have to attend work or even a party of their own?