I'm on my fourth bass from Rob and all have taken longer than initially projected. Three out of four have been custom but my first, a stock Solid 4, probably took the longest. Not meant as a complaint, just the way it is.
When I spoke to Rob in March regarding my new bass, my most customized to date, he felt it would be done in fairly short order, 3-5 months, which surprised me. I inferred that his workload at that time was pretty manageable. Since then I can see that the schedule is slipping which is why I assume his workload has picked up.
I learned long ago not to stress over build time, it will be ready when it's ready and it will be well worth the wait. I normally don't even ask for schedules on any custom gear, the only reason I asked Rob for a guesstimate this time was so I could plan my "accumulation of funds" in the coming months