I did the D-316 keeping test mentioned here:
I started this before I knew there were 2 forms of the metaborate, 4-mol and 8-mol,aka Kodalk of which 1.354 times the weight is needed.
The form I used was probably 8-mol Kodalk ,it is not labelled on the old pack but looks like some known Kodalk I bought later.
So 8-mol is probably good for at least a year but I cannot say for sure.