If you tell them you're going to retake, they will wait to fully process your application (regardless of your score the first time).
If you wait until you get your August score to submit (October), it will be almost too late for most MD schools. This is not a strategy to follow unless you expect to be a super-competitive applicant who schools will rush to interview. Better to submit early.
With a 23, you need to sit down and really look at where you want to apply, how much money you can afford to spend, where you are likely to get in (mdapplicants.com is a good source), and where you would be happy going to school. If the answer is, "I only want to go MD, I want to go to a specific school in a specific location, and I can only afford to apply to one school," then you need to be very realistic about your chances. Yes, you can get in to certain schools with the right application package and the right geography. If your desired school is UCSF, then you would have to be very, very special to get in with a 23. But if you are willing to apply to a wide range of MD and DO schools, and you can afford it, then go ahead.
Could you improve significantly from now until August? Depends a lot on what you did for studying last time. For many people, sure. You have nearly 8 weeks. But you would need to have great self-discipline, willingness to get right back in there and study, find and fix whatever went wrong last time, and it would really help to have an experienced MCAT instructor to help.