Truth be told, you will struggle to get someone to take a job for only five hours per week seriously. If you offer somebody a worthwhile income that makes a difference in their life, you might get a slightly better quality and more committed applicant. I say slightly better, because nobody really wants to be a cleaner these days, generally people will only do it as a stop gap job whilst they are looking for something else or developing other interests. Recruitment and staff retention is one of the most challenging issues facing the cleaning industry in general.
You could continue to find and take on new clients - but just defer the start date by a couple of weeks until you find a suitable cleaner. Many clients will be prepared to wait until you have someone in place. When you have a reasonable amount of work, say 16 hours or more, I think you'll find it easier to find someone suitable. Don't expect your staff to be as good or as dedicated as you (they almost certainly will not be); as the owner of the business you will obviously be much more motivated - as you are trying to build something for the future. Show them exactly what they need to do and how they should do it, don't assume they will know what to do. It might be helpful to produce an idiot-proof procedural manual so the work becomes as easy as painting-by-numbers; this will also help to ensure quality and consistency.
Even if you don't have enough work to begin with, you could always make up hours by getting your new staff member to do some leafleting or by helping out in other ways.