singapore001,
Not really sure what you mean down here, but if a SQ sponsored cadet can't pass their ATPL papers, he won't even get to go to JDK, let alone fly the Lear. So, SQ sponsored cadets are guaranteed a place in the L45 program after they pass their JDK phase. How soon though, is another story.
SiLLyMonKeY,
When you're referring to ATPL holders, I assume you're talking about self-sponsored pilots without any jet hours? If its direct entry FOs you're talking about, they can generally skip the L45 phase. However, if the company puts you in a L45 straight, it means he's still a cadet and so is no different from any ab-initio pilots. The only thing he'll skip is the ATPL and the JDK phase which would save him about 1.5 years.