Six inputs — hours, glass type, sun exposure, deposit state, bird diet, rain — and the chemistry says immediate, today, this week, or whenever convenient. Plus the removal protocol for the specific glass-and-deposit combination in front of you, and the forecast of when reversible becomes permanent.
one more sun cycle on a concentrated deposit shifts the verdict to immediate
The deposit is doing measurable etching at the current exposure but has not yet reached the irreversibility threshold for this glass type. Removing the deposit today, before the next direct-sun cycle on the panel, prevents the etching from setting permanently. The window is hours, not days, but it is real. The removal protocol below works against the time pressure.
A partially-dried deposit has an outer crust and soft interior. Direct wiping smears the soft interior across the glass and increases the surface area in contact with the acid. Lay a warm wet cloth over the deposit; leave it for five minutes; then lift the cloth and the deposit with it. Repeat if needed.
Standard annealed and tempered glass tolerate the house standard (warm water + dish soap) for almost all bird-soiling work. If the deposit resists a thorough soak-and-wipe cycle, an alcohol-cut mix (50% water, 50% isopropyl alcohol) is the next rung. Do not use ammonia, vinegar, or commercial "bird poop remover" sprays — none of them are necessary, and several can leave a worse mark than the deposit itself.
After the soak, lift the deposit with a single light-pressure wipe in one direction (top-to-bottom or left-to-right, whichever the deposit pattern suggests). Use a fresh face of the microfiber cloth for each pass; do not reuse a soiled cloth section. Scrubbing back-and-forth grinds the partially-dissolved residue into the glass and is the most common way a removable deposit becomes a permanent mark.
Once the deposit is lifted, the panel still carries the dilute uric-acid residue across a wider area than just the deposit footprint. A normal cleaning pass (squeegee + house standard or whatever the routine cleaning is) removes the spread residue. After the clean, look for any remaining ghost outline of the deposit — that ghost is etching, and it is the signal to schedule a glass-coating inspection on coated glass or just to accept it on annealed.