The correct time to leave a cleaner in the bowl depends on the product. Longer contact is not automatically more effective.
Read before applying
Check the product label for the intended surface, amount and contact time. Some cleaners are meant to be brushed and flushed promptly. Others specify a defined dwell time. Use the directions for the exact product you own.
Avoid leaving an unknown product overnight
An extended soak can be unsuitable for certain finishes, fittings or cleaners. Do not assume that a product designed for the bowl can also be placed in the tank. Ask the manufacturer if the instructions are unclear.
Keep products separate
Never mix toilet cleaning products or add another cleaner over a product already in use. Provide ventilation as directed and keep the area inaccessible to children and pets while cleaning. Store products in their original containers.
Address recurring marks appropriately
If marks keep returning, identify whether the cause is mineral buildup, staining or an underlying maintenance issue. Choose a compatible treatment and follow its instructions. A longer exposure should never substitute for selecting the appropriate product.