Hi there, if I understood what you want I guess this would do the job.
Create you tex layer then apply this expression to the source text parameter:
if (time < 4) random(1,10) else value;
This will get random numbers untill it reaches 4 seconds and then stop at the text you want.
You can off course adjust the values.
If you want them to come one by one to the final value I guess there is a text preset already for that.
I hope I could help.
Cheers.
ninguem.