Nothing is ever too homemade IF it works correctly. We are all big DIYers here at TFP.

But here are my concerns. By my calculations using PoolMath 9 gallons of 10% bleach=1152oz which per PoolMath would raise your FC by a total of 49ppm. Assuming the water and bleach are going in in the exact 50/50 ratio, which is highly unlikely because the bleach is heavier and will probably settle to the bottom of the can, so I suspect you'll probably end up getting mostly water for 15 days, and then mostly bleach for 15 days or vice versa.

But let's pretend for a second that all is going as planned, and you are getting 3 oz per hour=72 oz per a 24 hour period (again, only 1/2 of that being chlorine and the other half being water).

If you divide the total that those 9 gallons can provide weather mixed or not which=(49ppm), by the 30 days you are gone, it equals out to an approx. 1.63 daily FC level Only, which isn't enough to maintain your pool at the recommend 3-5ppm level for your 40ppm CYA.

Now if everything went as planned and you had 18 gallons (2304 total oz) of chlorine, instead of just 9 gallons in there running at the same rate then it could provide a total of 97ppm of chlorine. If you divide that by 30 days, and that would put you right at the minimum FC range of 3.2PPM daily for your current CYA level that Might be being added to your pool correctly. If something doesn't flow exactly right, or the concentration depletes, or it rains while you are away raising your chlorine demand that isn't in there then I suspect you will most likely come home to a nice green pool.

I think your initial idea isn't supplying near enough daily chlorine, and even doubling the amount, as in my example, is still cutting it way too close for comfort. I hope this helps, and have a wonderful day.