My personal suggestion is to spend those five hours as a freelancing nomad by giving unsolicited support to any charity, business or individual which can provide career capital or simply philanthropic results from your work.
A project which both does good while also allows for the flexibility of reconnoissance and growing career capital. It sounds like you might be best freelancing. The book Surrounded By Idiots puts forth four professional personality types (https://www.penguin.co.uk/articles/2019/jul/surrounded-by-idiots-personality-types-at-work.html - a great system for simplifying choices and predicting business interactions!). I suspect you are mostly blue, in which case simply doing some freelance, unsolicited market research, data analysis or trend analysis for a charity are your best bets in terms of doing good while also maintaining the flexibility of growth (career capital) and autonomy (reconnoissance). You can freelance simply by researching -as you already are doing to answer your question- areas of interest for charities. You can make some assumptions (such as 'all charities need market analysis' and 'all charities lack effective partnerships', both have held true in my experience), or you can outright ask any of your favourite charities and give examples of what you might do for them.
However, if you/your friends are mostly yellow, like me, don't settle on one project; you won't thrive with repetition!
As someone who changes focus more frequently than is effective, I found traditional volunteering didn't work for me and, as I was finding my skills, I couldn't commit to long project stints. So I made my own opportunities by doing small favours for my favourite charities. Whatever interest I would be focused on at the time, be it journalism, networking, businesses analysis, marketing or graphic design, I'd do a piece of work for my favourite charities and email them my efforts. At times this wasn't well received but it was no effort on their part to say they didn't want my output. On the other hand, I found some great opportunities to do other odd jobs for charities and businesses and it lead to forming my identity as a networker of c-suite members and free gamification provider for charities; neither of which you can learn if you're committing to a single project for another organisation. However, being your own boss isn't for everyone.