visa process (Riyadh)

Hello all! I am a Briton potentially moving to Riyadh with a srart date of 1 September Protected content .
My employer has stated they will send over all documents in August for the visa application.
I'm confused as to why they cannot process the application in advance as it is only May now. Does anyone if the application can be done sooner?
I want to hand my notice in to my current employers but I'm worried my employers in Saudi may not honour my new contract and/or that my visa application may be unsuccesful...

Please advise

Thanks Mohamed