Honest answer: no, the strict every-two-hours cadence is not built for your situation. Reapplication guidance exists because sunscreen rubs off, sweats off, and degrades during meaningful sun exposure — the AAD's framing is every two hours outdoors, and after swimming or sweating (https://www.aad.org/public/everyday-care/sun-protection/shade-clothing-sunscreen/how-to-apply-sunscreen). A day at a desk isn't that.
What window light actually does: standard glass blocks essentially all UVB (the burning wavelengths) but lets a meaningful chunk of UVA through — the deeper-penetrating wavelengths tied to photoaging and pigment. So a morning application of a broad-spectrum sunscreen is doing real work if your desk gets direct sun, and topping up around midday is a reasonable extra if you're literally sitting in a sunbeam — but there's no evidence-based need to scrub and reapply hourly indoors.
The part worth keeping sacred is the daily habit itself: in the randomized Nambour trial, it was consistent daily use — not heroic reapplication — that produced measurably less skin aging over 4.5 years (https://pubmed.ncbi.nlm.nih.gov/23732711/).
One caveat: if you're managing melasma or stubborn pigmentation, visible light through the window also matters, and ordinary UV filters don't block it — a tinted sunscreen with iron oxides does (https://pmc.ncbi.nlm.nih.gov/articles/PMC8887048/). Otherwise: apply generously in the morning, reapply when you actually go outside, and spend the reclaimed anxiety elsewhere.