I use a visa debit card and withdrawals are instant 24/7 now, used to be next working day at around 3:30pm.
remember though you have to wait for them to process it, it might still be 'pending' on the site, I'm guessing not all sites do automatic withdrawals.
also about the two halves thing, possible your deposit was instantly refunded and the rest will be manually sent (pokerstars do this method )
example: 2 days ago I deposited £20 and lost, yesterday deposited £10 and won and withdrew £80, £30 was paid instantly (deposit refunds) and the rest (£50) was manually paid about an hour later.
All my withdraws at pokerstars to paypal are always instant. I rarely get the occasion when it splits it up. Played there for about 8 months now and I think it has only happened 3 times. The second part on all those 3 times still only taken a few mins....
This is the main reason I play there plus they have the races too
I think the manual additions are needed in my case because I have actually withdrawn more from pokerstars than I have deposited there, it would normally be refunded instantly from past deposits.