Hi Shashi
You will have to wait till the first Costing Run completes, if the no. of cost estimates involved are more than 5000
For this reason, I used to schedule it as a Background Job for Plant 1 - Batch Job name ABC123
Similarly, schedule the job for Plant 2 and give dependency on 1st Job.. The 2nd Job will start as soon as the first job completes
OR
You can give an estimated start time for the 2nd job, which would cover the completion of 1st job
Ajay M