@DavidRoss91 All the performant guardrails for segmentation and profile will come to play for global segmentation job. you need to adhere to these to have optimal evaluation duration, If you can't resolve those near time, I would recommend to reach to Adobe to get added more processing power or move your tenant to siloed environment rather than shared environment.
https://experienceleague.adobe.com/en/docs/experience-platform/profile/guardrails#segmentation-guard...
I have this case with one of my client in the past and we moved to siloed environment to keep the global job to defined duration to match with business requirement.
Let me know if this solves your concern.
~cheers,
Naresh Nakirikanti.