Does it do my scars any use if I wld to apply lightening cream for 1 hr n then washing it away? Thanks!

Not really. Scars are permanent, and lightening creams won't really change that. If you have a scar that is thickened, discolored, puckered or otherwise extra unsightly, consult with a board-certified plastic surgeon to discuss what treatments might be an option for your particular scar & skin type.
Probably very little. Scar lightening creams are generally applied overnight to allow sufficient time for action while sunblocks and/or silicone gel are applied during the day.