How often does Zara get new stock?

[Spidergirl8]

I'm looking for a smart backpack for the office that doesn't look anywhere near a hiking one! Preferably one that is more handbag in style iykwim. Anyway, a few web searches have brought back lots of lovely Zara ones that have sold out or were from last season.
Rather than taking a risk on Ebay I thought I'd wait and see what stock Zara may bring in for autumn/winter. Does anyone know how and when Zara bring in new stock?

I think they get weekly stock deliveries?

I'm not a backpack person but I saw this on the Wearing It Today blog recently: www.marksandspencer.com/leather-rucksack/p/p22319178

Thank you! I'm not a backpack person either, just juggling the nursery drop and work bag is becoming too much of a struggle!