As of December 9th, 2015, Steam requires all users to enable Mobile Steam Guard and trade confirmations. Without these two things, all your trades will enter a 15 day escrow period where the items will be held by Steam. At the end of the 3 day period, if you have not asked Steam to cancel the trades, the items will be delivered to the recipient. Note that the Escrow hold only applies to trades in which you send items.
If you are receiving items, trade holds depend on the sender's Mobile Steam Guard and trade confirmation status. All item withdrawals from BitSkins are instant.
Yes. Escrow does not apply to folks only receiving items in trades. You can purchase items, and withdraw them instantly.
This is the three-day Escrow period described above.
You either did not have Mobile Steam Guard enabled for over 7 days, or do not have trade confirmations enabled (see above). Once you do have both the Mobile Steam Guard and trade confirmations enabled, you will be able to list items for sale instantly at BitSkins.
As of March 9, 2016, trade confirmations are automatically enabled.