1. Depends on whether it's an essential variable or not - codes/standards differ on this issue. Essential then no. Non-essential, with appropriate people involved, documentation of deviation, revision at least in process if approved and communicated. What must the welder do? Often this is covered in the procedure or specification. Requirements may include that the welder must reheat the joint to a specified minimum temp. Were there any preheat requirements to begin with? Those may be applicable as well. How much thickness to be deposited before welding is delayed may also be an issue. Joint restraint, alignment stresses may be factors - material type and welding process/electrode selection as well.

2. Production welding or during the WPS qualification? Assuming there is documented instruction such as in the written WPS, from an inspectors perspective I would follow what the requirements are, if any. During qualification, this may be an opportunity to document the delay in weld passes and include that into the WPS if all factors are weighed and are deemed reasonable.

3. Cracking. It's one way to prevent cracking. When all the factors are considered for certain joints, conditions, welding variables ect...strict criteria may not be necessary for every situation. In either case, strict criteria or not, this should addressed during the qualification process when required. If you say for example, time between this pass and that pass can be 72 hrs or unlimited but the PQR has documented only a couple of minutes, how would you know this delay is adequate? We're talking multi-pass welds here. So, probably some things > than .500 wall. Accelerated cooling and other issues come into the picture. Have you increased the chances for hydrogen cracking? What about stresses? If welding was delayed, was NDT involved to verify quality before welding resumes? Not all situations have high risk factors. But some do. Address those.