After making 88 plus hour glass blocks, I thought I would share a tip that really helped me keep my corners in line.
If you're interested in making some hour glass blocks I would highly recommend the tutorial from Cluck Cluck Sew seen here.
First you will need to create the "two-halves" of your double hour glass. Do not iron yet!
Take the first half and pick a side that you will start to press first. You will not be using open seams and so you will want to start each side from the same fabric. Below I decided to start on the side with the Kona Oyster.
Press carefully, but not too hard that you stretch your fabric. Repeat this step with the second half of the block. Remember to start pressing from the same colored fabric as the other half.
Now you have your two halves of your block.
Because you pressed both halves in the same direction, your seam is now on the same side. When you go to match your seam / corner, you now have the creases of the fold to help you.
The creases can be pushed together to help you align the center. Pin and sew the two halves together.
Press the seam either to the side or open, depending on your preference.
Trim the excess and admire your awesome block centers!
Repeat as necessary for your project!
If you have questions or suggestions for improvement, please let me know!