What the message means
The oil change page lists an "Engine oil service due" message in iDrive or the cluster, a Condition Based Service (CBS) countdown reaching zero and an oil level warning between services. It covers B46, B48 and B58 cars such as the G20 330i and M340i, F30 340i, G30 530i and 540i, G01 X3 and G05 X5. See Oil Change / Oil Service.
We have not found a sourced mileage or month interval to quote, and we do not repeat unsourced numbers. Treat the cluster message as the trigger and check your owner's manual or a dealer for the figure on your car.
Value Service pricing
The page says four-cylinder cars often qualify for BMW Value Service pricing at participating dealers once the free maintenance period ends. Eligibility varies by dealer and model, so ask the dealer whether your car qualifies, because the four-cylinder price is much lower than the standard menu. The job takes under an hour of shop time.
Oil spec and the right engine
Confirm the correct oil specification for your engine: many G-series cars call for 0W-20 LL-17FE+. The N20 timing chain page recommends BMW LL-01 5W-30 as a related part, which is a different spec on a different engine, so do not carry one engine's oil to another (N20 Timing Chain & Guides).
If the level drops between services
An oil level warning between services is worth taking seriously. The N63 valve stem seal page lists burning about a quart of oil every few hundred to 1,000 miles with blue smoke (N63 Valve Stem Seals), and leaks are covered in the BMW Oil Leak: Common Causes by Engine.
Other services on the same visit
Brake fluid, coolant and transmission fluid are separate services with their own pages: Brake Fluid Flush / Service, Coolant Flush / Coolant Service and ZF 8HP Transmission Fluid Service, and the BMW Brake Fluid Service: When It Is Due and What It Costs and BMW Coolant Change: Long-Life Coolant, Flush Service and Bleeding go into each. For a map of the preventive items owners report, see the BMW Service Intervals Owners' Report: Fluids by Mileage.