To my knowledge Gulf Air and Jet2 'flywize' implementations were both achieved on time and within a short period from contract signature. It is all down to good management of the project. I know that some customers took much longer but that is equally true of other flight planning vendor transitions. Methinks that many of the problems that airlines experience in cutting over to a new flight planning system are of their own making.
If you know about the QANTAS/LIDO debacle then you will understand that anything is possible (or not).