0% purchase card

I want to a big purchase but dont want to pay in one go so would like a 0% credit card that allows me to pay off the purchase over a 6-12 month period.

I would like to apply for either of these cards, preferably TSB:

http://www.tsb.co.uk/credit-cards/landing-pages/tsb-card/?WT.mc_id=1588409|119744314|292549981|0&so=MON_2020

https://www.halifax.co.uk/creditcards/balance-transfer-and-purchase-card/

However the summary's state very similar things that are confusing:

Purchases: 0% p.a. fixed for the first 24 months from account opening.

but then go on to say:

Interest-free period: Maximum 56 days for purchases if you pay your balance in full (including any balance transfers and money transfers) by the payment due date and you also paid your previous month's balance in full by the due date.

Can someone explain the above as it seems to contradict itself?

Thanks!