Same-day bookings are usually possible: if you order in the morning, a cleaner can be at your door within a few hours. Still, the earlier you book, the more freedom you have in choosing the time.
A day ahead is enough for an ordinary flat on a weekday. For Saturday, for the last days of the month and for the end of December, book three or four days in advance — those are the busiest slots in Kyiv, and the convenient morning windows go first.
Large jobs need more notice. Post-renovation cleaning, a house, dry cleaning of several items or a flat that has stood empty for a long time require a team and specific equipment, so plan them about a week ahead.
Moving out is a separate case: agree the date with the landlord first, then book the cleaning for the day before the handover, not for the same morning. It leaves room if the keys are handed over later than planned.