The short answer
Choose a window-cleaning interval around the finish you want, how quickly your own windows become dirty and the scope of the visit. Compare a first clean and a recurring arrangement as separate decisions.
Use your windows as the reference
Observe the glass between visits rather than treating a generic interval as a requirement. Exposure, nearby activity and the parts of the home that matter most to you can affect when you want another clean. Tell the provider whether your priority is an occasional refresh, consistently clear front windows or a regular whole-property visit. Ask what interval they suggest for that brief and why.
Ask about the initial visit
A first clean after a long gap may involve a different scope from ordinary maintenance. Describe built-up marks and include close-ups. Ask whether frames, sills and doors are included and whether specialist residues need separate assessment. A recurring per-visit figure is difficult to compare if one quote assumes a more extensive initial clean and another does not.
Compare the arrangement, not just the interval
Confirm the included windows, price per visit, expected schedule and access requirements. Ask how you will be notified and how changes are handled in WhatsApp. If rear access will sometimes be unavailable, agree what happens to those windows and the price. A shorter interval is useful only if it matches the result and ongoing commitment you want.
Review after experience
After a few visits, assess whether the windows stay at the standard you want between cleans. Discuss a different scope or interval if necessary and keep the change in the conversation. Do not assume a one-off booking creates a recurring arrangement or that a recurring arrangement includes occasional specialist work without it being agreed.