Does anyone know how long it takes for Apple to run a diagnostic test on a MacBook Air and typically how long does it take them to repair issues such as Hard drive lid sensor and whatever else they may find?
You can perform a hardware test at home (an Apple Store or AASP will do the same thing initially anyway).
Use Apple Diagnostics to test your Mac - Apple Support
It will at least give you an early heads up as to what the issue may be before taking any further steps and may even indicate that you really don't have a hardware problem but some software/firmware/OS issue.
I'm afraid, only the Genius Bar at an Apple Store or an Authorised Apple Service Provider might be able to answer that.
Ingo2711 is right. We are other end users, not Apple.
If repairs are indicated, understand that few repairs are made in-store now. The sealed nature of many Apple devices and the nightmare of inventorying parts for hundreds of variants with one product group make while-you-wait service impractical.
Depending on what is needed, most stores will send the device to a centralized Apple repair facility.
It may be better to start by describing here what issues you have. Many of us have been working with Macs longer than some Apple store employees have walked this earth.
Be sure to include your Macbook Air's SUB-MODEL, screen size, and macOS version. Doing "About this Mac..." gets you that info:
MacBook Air diagnostic and repair time estimates
