There's no fixed day or week when biotin starts "working." People usually take it daily over a long stretch, any effect is gradual, and experiences vary a lot from person to person. So it makes more sense to think in months than in days.
Think in months, not days
Because the change is slow, taking biotin only now and then makes it very hard to tell whether it's doing anything for you. If you're already wondering about it with the first bottle half empty, that's a common place to be.
A fixed daily time, like breakfast, makes the habit much easier to keep for the weeks and months involved. Many people say the first few weeks feel uneventful, and that seems to be normal. A gradual process like this doesn't produce a dramatic before-and-after early on. Instead of checking every morning, pick a longer interval, maybe once a month, to ask yourself whether anything feels different. Day-to-day fluctuations are hard to read anyway.
Staying consistent long enough to judge
Consistency is the whole point, and seeing your daily record helps you stick with it long enough to have an opinion. Pillog lets you check it off from the notification and see your month as a single card, all kept on your phone with no account and no ads.
Missing a dose here and there is common and probably not worth worrying about. A pattern of missed days over several weeks is different. It makes it much harder to say anything meaningful about whether the routine is helping. That's the practical value of a simple log. You're not tracking for the sake of it. You're giving yourself an honest record to look back on, because memory over a span of months isn't very reliable.
Starting small and adjusting as you go
A lot of people find it easier to start at the lower end of the suggested amount and get the habit down first. Once taking it every day feels automatic, it's easier to notice whether anything needs to change. Tying it to something you already do, like brushing your teeth, making coffee, or your commute, means one less thing to remember on purpose.
Biotin is also only one piece of a bigger picture that includes diet, sleep, and your overall health, so its effect can be hard to separate from everything else. If you have specific concerns or take other supplements, your doctor or pharmacist can give advice that fits your situation.