Firstly, nothing you have said is going to guarantee a tip, because there is no guarantee to get a tip.
When I am the buyer, I want the work done to my specifications, not some artists rendition which has no bearing on my requirements. Your idea might work if the request is to create multiple versions of a logo or something like that, but this is far from axiomatic.
Can you give us your formula for how fast to work? It seems to be something like Delivery Time < .5 Gig quote > .2 Gig quote, where Gig quote = 10
Again, you are making generalizations. Your gig quote should align with the time you know it to take to do the work, plus a little cushion for revisions if offered. Setting your gig quote at 10 days when you know you can do it in 5 is probably running off more buyers than the repeats you will get for delivering early. Additionally, that will only work with a given buyer once or twice and then they will know you can deliver in far less time than you quoted and it will become the new expectation.
I cannot emphasis enough how incorrect this is for many, many buyers. Personally, I will not buy from someone who offers unlimited revisions because it means they have no confidence they can deliver the correct product the first time. There are many threads in the forum detailing why this is a horrible idea.