You may already be aware that booking the W and Circuito Macizo Paine (O) treks can be kind of a nightmare. If not, then you’re aware of it now!
The popularity of the park means that places at the campsites and refugios start to book up extremely quickly for the summer months (December – February). Therefore if you have set dates for your trip it is advisable to book as early as possible, ideally when booking opens. This is more problematic for longer term or last minute travellers, who aren’t sure when they’re going to reach Puerto Natales. The option then is to check online availability once you have a clearer idea of dates and if that doesn’t work out to try to book in Puerto Natales, which IS still an option.