haha, kwoni, in the construction industry, from piling, external structure building, internal wall structure building, electrical and plumbing installation are all done by different department. i.e to say, while you see the blk being built up, the electrical and plumbing engineers are there to oversee the electrical and pipe installation.
everyone are doing their own job and they will be doing all this concurrently. also, contractors will not wait till all 4 blk are ready then hand over the keys to u. once any of the blk is ready with all the installations and check done, they will release the keys to u. this is the usual practice hdb is doing all these years.
based on my experience, to be frank, i have confidence the blks can be ready in 2009. the first blk of keys could be released from june 2009 onwards. like wat i say earlier, unless due to unforseen circumstances...
safety checks will be very fast. if the contractors are efficient, in fact within a week they can finish all the checks.