Machining is rarely the constraint. For a typical programme the time goes to material reservation, sampling rounds, approval, and — for markets with documentary credit — banking. Cutting and polishing a few thousand beads is a matter of days; agreeing what those beads should be routinely takes weeks, and waiting for a letter of credit can take longer than both combined.
This is why we plan backwards from your delivery date rather than forwards from the purchase order, and why we ask early who holds authority to approve the physical sample. A programme with one named approver moves at roughly twice the speed of one run by committee, and that difference is entirely in the approval stage rather than on the floor.
Where a date is genuinely immovable — Ramadan, a national day, a summit — we name the point after which the timeline stops being achievable and we say it while there is still room to change the specification. A supplier who agrees to every date and explains afterwards has cost you the option of a smaller diameter or a simpler furniture specification that would have made it.