There is no set amount of time. The IRS frowns on entities failing to generate required Forms 1099 and W-2, so contacting the IRS as indicated in Tax Topic 154 might result in the IRS contacting the plan:
https://www.irs.gov/taxtopics/tc154
Otherwise, submit the substitute Form 1099-R (Form 4852) on which you are asked to describe your efforts to obtain the required form. I believe submitting the substitute form precludes e-filing, so you'll have to mail your tax return.
