I did my first test time lapse using qDSLRdashboard, and processing in LRtimelapse. I read somewhere the intervals should be about double that of your shutter. I started off at 5 second exposure at night with a hard 10 second interval over 8 hours. Those 85MB photos were not fun to process, and I ended up just speed ramping through most of them anyway to get it to a 10 second play time.

My shot had traffic in it, so having a longer interval seems like it would be stuttery. How do you get that silky smooth time lapse than compresses a day into under 15 seconds?

A day in 15 secs? Where did you see that? In most of the cases this won't look sikly smooth because too much movement happens during a day (clouds etc.).

The 180° "rule" is more a recommendation to use longer exposures. When doing the holy grail, and ramping exposure, of course you can't stick to that recommendation.
I'd reformulate the rule like this: use the longest exposures you can - if you can. For Holy Grail, often you'd have to shoot with shorter exposures also, because you won't be able to change ND filters while shooting.

Thank you for the help. How much do you violate the 180 rule before it starts looking janky?

You cannot say that. It depends on how fast the movement in the sequence is.
If you have people or cars passing by quickly you should definitely stick to long exposures, but if it's a peaceful landscape scenery you won't see the big difference (apart from insects an birds popping up with short exposures).
All in all long exposures should be preferred, but no rule that can't be broken.