How long should a basic service actually take?

Simple question that I somehow don't know the answer to. I've had services take anywhere from two hours to two days depending on the place, and I've never understood why there's such a huge range for what's essentially the same job. Is it parts availability, staffing, how thorough they are, or just disorganisation? I've been looking into fast Jeep service and maintenance in Musaffah Shabiya hoping to find somewhere that's actually efficient without being sloppy, but "fast" and "good" don't always go together and I'm wary of places that rush and miss things. For those who get their Jeep serviced regularly, how long does it usually take at your place and do you feel like they're being thorough or just quick? Trying to set realistic expectations so I stop being annoyed every time.