The honest answer is that it depends on you more than on me
I won't give you a number of weeks, because it would be a made-up number, and anyone who gives you one before having seen your process is guessing with the air of someone who knows
What I can tell you is where the time goes, and the surprise is that the technical part, meaning writing the system that opens the screens, reads the documents and fills in the fields, is the most predictable part of the lot, you look at the process and you can see roughly what there is to do
The four things that really stretch it out
The first is the unwritten rules, the ones that live in the head of the person who has been doing the job for eight years, and that turn up halfway through when the case that fits nowhere arrives, you ask how it's done and the answer you get is it depends, and that answer is sincere
The second is access, the account to get into the business software, the portal credential, the permission somebody else has to grant, and until they arrive the work stands still even when everything is clear
The third is the person who knows the process, who is always the busiest one in the company, and finding half an hour of her time is harder than writing the code you need
The fourth is the odd cases, and those don't come out by talking about them, they come out by trying, the supplier who writes the amounts his own way, the invoice with no order number, the file that turns up that month with one extra column, every case like that is a piece of work you didn't know you had to do
None of the four is anybody's fault, they're what a working company is normally like, and a supplier who promises you precise timings is pretending they don't exist
What you can do to make it shorter
There are two things you can do, and they're worth more than any promise of mine
The first is to name one point of contact, only one, the person who actually does the process and not the one who describes it from above, and to put her in a position to answer when needed, without having to ask permission every time
The second is to send the sample documents straight away, not the three cleanest ones, the real ones, including the two that make everyone swear every time, because that's where you see how much work there is, and they can be made up or blanked out if there is customer data inside
Then there's a third thing that helps and costs nothing, telling us about the crooked cases that have already happened instead of hiding them, keeping them to yourself to make things look simpler stretches the timeline, because that case turns up anyway, only later and more awkwardly
If you want the full list of what to have ready, it's in the guide on what to have ready before you start, while how it works has the whole round from the first contact onwards
One thing I'll say plainly though, the time doesn't end with the rollout, the automation starts out alongside the person and becomes autonomous little by little, and it's like that on purpose, it's the only way to bring out the cases nobody had mentioned