I was just going on Clare's latest version of her treatment algorithm (recommendations for vets), which omits mention of frusemide and recommends two other CSF reducing drugs. At the top she says 'Start CSF pressure reducing drugs e.g. cimetidine (Zitac) ... orally 3 times daily' and at the bottom she has a note: 'Because cimetidine reduces stomach acid it may reduce the absorption of other drugs. It is recommended that other drugs are administered at least 2 hours before the administration of cimetidine.'
I would guess that Harley is only on twice a day because he so far only has a pre-syrinx, and Clare always seems to recommend starting drugs low, and the time gap doesn't apply because he's not on other drugs (such as gabapentin).
Kate, Oliver and Aled