Looking for advice l: competition between adventuring parties

[Baron Opal II]

When I do things like this the most important thing to me is the time scale. I would run the adventure for the adversarial party in broad strokes. This way I know when and where they are, and thus what the PCs will hear and encounter. I'm not rolling every die, just getting a feel for the tempo.

 

[Fenris-77]

You can also use the opposing party as something like a clock. They have their own information and motivations, and sometimes I'll schedule events in the background to happen regardless of party actions. Just roughly, but I want the PCs to feel like the other party has it's own 'life' and timeline so to speak. To make that happens I'll use timestamp type info to help give the PCs a sense of how far behind they are, and I'd also make sure there is an explicit "you just passed them and are in the lead" moment should they pull into the lead. Signed and dated notes left at key locations and mocking the PCs for being slow is fine way to get this done.