Having a contract for a job is not the same as being allowed on the job site. Plenty of locations will not allow you into the work area without a specific credential, a background check, an orientation, or an escort, and every one of those carries a potential lead time. All of which need to be completed before you can even step on site, let alone mount an access point.
A few necessary credentials that may turn a one-day install into three weeks of extended effort:
Rail or active track: background screening plus railroad-specific safety orientation, often a flagman for track clearance. Budget weeks.
Hospitals: an Infection Control Risk Assessment (ICRA) permit, fire-and-egress protection during work, badging, and escort. Many systems want ICRA-awareness training first.
Schools and childcare: a background check and/or fingerprinting, and work pushed to after-hours or break-time only.
Data centers and correctional sites: escort, change-control windows, NDAs, tool control counted in and out.
Every requirement on this list is set by somebody other than you, and rarely will one of them show up in the scope of work. They show up the week you planned to do the job. That is why we built this PDF document as a way to help you prepare, so the timeline you agreed to is the timeline you can meet.
Download it, print it, and run over it as you write a quote rather than after you win the deal.
Which access requirement has blown up a schedule on you, and how far ahead did you have to start it?