On Bitshares you don't have to withdraw funds. You just convert open.BTC to bitUSD. Everything takes 3 to 5 second.
Check his site: https://bitshares.org/
Read link: Price-Stable Cryptocurrencies, where assets pegged to Bitshares token is explained.
All your funds stays on Bitshares blockchain, can't be hacked or stolen, if you secure your password and master key.
Complete new world are this decentralized exchanges (DEX). Very cool stuff, go and check it!
And follow me I write a lot about Bitshares DEX and stuff alike.
RE: Kraken withdraw in less than 24h, what about coinbase and other exchanges?