Procuring materials with different delivery timelines

Hi all,

I referred to many threads did not get exact answer and i am new to MM.

My customer orders few materials which are having high lead delivery times well before BOM is built based on forecasting and confirmed orders received. Now they are moving process according to which they need to order any material only after BOM is received from engineering tool. So now problem is by the time they get bom which has this materials which take long time to get in to stock the production time line will increase. Because they order after BOM is received and few of materials in bom take long time and few take shorter time. Does SAP has any best process to handle the same.

What i understand is we can put planned delivery time or lead time in MM which can raise PRs based on this time line put here but i am not able to synchronize between long lead items and short lead ones.

What customer wants: By the time BOM reaches SAP from design tool some how long lead materials should be ordered and short lead can be ordered after BOM in SAP.

So can some suggest me best model which can be followed for this