Solution : https://service.sap.com/sap/support/notes/31248 (SAP Service marketplace login required)
Key words : 
long run times occur, additional key words vkm1, rvkred01 vbak-amtbl, sales documents, checkbeing carried, availability check, credit check, solution corrected, prerequisites, p22k011945
Related Notes : 
       
| 53201 | Availability check during release | 
| 52272 | Availability check during release | 
| 36429 | 3.0C: No purchase order req despite credit release | 
| 35047 | Conf.qnty, credit limit check, transf.of reqs. | 
| 33103 | Credit check, availability check, performance | 
| 33078 | Credit check: Blocked documents are approved |