No, you don’t have to wait for an AGM. You make a submission to the strata committee to do something about the heat, including the suggestions you have listed here and maybe even some idea of costs.
You could also include the fact that you have been contacted by several residents who agree (no need to say there were only four).
And you could politely ask if the owners corp doesn’t have a duty to arrange for someone to clean these windows (it does.
If the committee refuses to do either thing, or just doesn’t respond, your next step would be to call for mediation at Fair Trading and take it further at NCAT if that didn’t work.
But at some point, someone will tell the committee it’s easier and cheaper just to fix the problem than fight the issue then have to fix it anyway.