You should start feeling the pain-killing effects of ibuprofen or paracetamol tablets about 30 minutes after taking them. This is the time it takes for them to be dissolved and absorbed by the stomach.
Ibuprofen is also an antiinflammatory and it can take up to three weeks to get the full anti-inflammatory benefits to relieve chronic conditions such as arthritis. Don't forget that ibuprofen should be taken with or after food to prevent it irritating the stomach lining.
Taking ibuprofen or paracetamol in a liquid, soluble or gel form can help - this is because gels or liquids are easier for the stomach to digest as the medicine is already dissolved so it can start working sooner.