There is no real "right way" to use hypo, except in the safety sense. Dont spray it near/on lawns or flowers. Wet down any lawns/flowers nearby before you use hypo and keep the lawn/flowers wet throughout. (or cover if possible).
Some guys on here turn up to the job, wet the area, and lather it with hypo before they clean. Me personally, i turn up, clean the area, then see what needs attention with the hypo and treat those areas accordingly. Personally, i use the hypo until the areas are clean, then i leave it on, and warn the client.
If i think its going to cause a problem i tell them to stay off it until its dry, or i use my judgement and might not even bother using it.
Its all trial and error, i know i came on here and didnt know what hypo was, got a bit of info from here, and had a few informative phonecalls from some other guys on here giving me some tips (similar to the tips above) and i learnt as i went. I killed an old womans lawn cause i used too much and too neat, but i still clean here patio.