For me, Umbraco will frequently hang, freeze or timeout when I try to save edits I have made to a Document Type. Luckily, there is a workaround. Instead of making your edits via the GUI, use the Export/Import Document Type instead.
Step 1 – Export the Document Type you want to edit.
Step 2 – Edit the xml. You can export other Document Types if you cannot find the attributes you want.
Step 3 – Import the Document Type.
I have been using Umbraco the past few months with little trouble, except for this problem. Is seems quite rare, as I could find nothing about it on the Umbraco forums or online.