I've bonded with Blobssom in Dara's Darlings for two days now but I haven't been given an option to buy it, only to continue bonding with it... Do some minions need more time to bond to you before you're allowed to buy, or is mine bugged?

yes, certain minions can only be bought after bonding with them for the maximum number of days.

Thank you, I hadn't gotten a minion that needed extra bonding time so I didn't know.