When the page loads, Sprwt takes now + Order Buffer Time (if none is set, +5 minutes), looks at today's Real Time windows sorted by start time, and picks the first moment that is inside a window (or the start of the next window if the current time is before it). That time is pre-filled in the time picker. If the customer already had a valid time in the cart for that day, that time is kept instead. If no window is left today, the customer sees the "no meals available" page.