800 mg of ibuprofen at once is safe to take.
So you can safely take 800 mg of Ibuprofen at one time but then you'll need to wait a bit longer to take another dose of 800 mg of Ibuprofen.
For adults or those 12 year of age or older it's safe to take up to 3,200 mg of Ibuprofen per day and as long as you do not exceed that dosage you will be fine.
Once you take Ibuprofen it can take 30 minutes for the Ibuprofen to kick in once it's had time to go through your system.
Sometimes Ibuprofen works as soon as 20 minutes after taking it but sometimes it takes as long as 30 minutes for the effects of Ibuprofen to be felt.
The pain or other ailment should start going away within 40 to 60 minutes of taking Ibuprofen.
Aleve usually works much better than Ibuprofen so with Ibuprofen you may need to take it every 4 to 6 hours to keep the pain away.
After taking Ibuprofen for any pain I have the pain usually starts going away within 60 minute of taking it and the effects from Ibuprofen usually last for me for a couple hours or so before I need to take another Ibuprofen later.