Since you will be getting the funds from the retirement plan

Since you will be getting the funds from the retirement plan, you should get some kind of written notification that you have applied and the money is being removed from the retirement account and will take XXX weeks to complete.

You can copy that letter and show it to your mortgage company, so they know you are not just lying for more time and stalling. They will more likely to wait for the money if they know for sure it is coming in a definite time, which will be set in the letter from the retirement fund.

Good luck!