I started using the Dave Cushman recipe years ago (have not checked if it is the same as Hivemaker's) and mix in my syrup before bottling in 2L water bottles.
In slowly increase the dosage in the syrup until my queens just go off lay, then cut back, but always add some in (min. 1ml thymolated mixture to 1L syrup) as it ensures the sugar syrup never goes off. I used no other treatment whatsoever last autumn on two of my hives as a test, with no adverse effects.
Any syrup leftover then gets topped up to the rim and the bottles get put in a dark spot in the shed.
I have kept full bottles of 1:1 and 2:1 syrup with Thymol added for over 6 months, (except for the bottle which fell over, rolled under the lowest shelf of a stack of shelves, and stayed there for 15 months, but was still fine) without any adverse effects, and the strength of the mixture seems to have also been unaffected.
The only other thing I have tried is using RO (reverse osmosis) water as it it is far purer than ordinary water, but the bees don't seem bothered either way. I use RO because I grow corals, and if I was to put tapwater in my tank it would kill them all fairly quickly due to the cocktail of chemicals in it (remember this is the stuff we drink). On the other hand, RO water is so pure it lacks any of the minerals or salts so vital for any life sustenance.
I can only assume this is why my bees started taking water from the wildlife pond I intentionally dug next to the apiary a couple of years ago, where the water is now a nice peaty shade of brown. A bucket of fresh tap water filled with straw (to avoid drowning) is not half as popular. (Maybe I could just dose the pond with Thymol and cut out the middle man - j/k.)
