Variations are where projects lose money and goodwill. Priced, sent and accepted before the work happens, they are a normal part of the job; agreed verbally on site, they become an argument at the final invoice.
The programme is set by what has to be ordered. Windows, worktops and made-to-measure units decide the sequence, and a delivery date confirmed late is what pushes a project into a second month.
Payment stages should track completion, not dates in a diary. A stage invoiced because the calendar says so, on a job that is running behind, is the fastest way to lose a client's trust mid-project.
Trades run in a chain. The plasterer cannot start until the first fix is done, and the tiler cannot start until the plaster is dry — so one missed day moves five other people and needs to be visible the moment it happens.