if we placed an online order for "click and collect", can we change our pickup time/date? i placed an order just now, but will not be able to pick up my piece until tomorrow as we live 2 hours away. if i don't show up, is my order cancelled?

I've just done this recently. You have exactly 24 hours from the beginning of your pickup window time. Make note of what you selected and when they say the ready time is. That's when the clock starts. After that it is put back into inventory and refunded to your method of payment within 8 business days. Hope this helps. =)

I'm pretty sure picking up the next day would be fine, but you should probably just call Ikea to double check

You should maybe call ikea to have this answered. But I believe they will hold the order for a limited time before cancelling.