I think ang major sayop diri nga thread is the word "planning".
When you say planning, that means agreed na ang tanan, nothing will change bla bla bla.
I've been into a lot of development and I dread the word planning. Because everytime I hear it, I think of your client nagging you about "change this, change that, I don't want that". Labi na if walay kasulatan or contract na that's final.
If you're writing this Payroll system from scratch (no existing system, whether computerized or not), prepare for that nagging.
If you're writing it from a framework, then you're onto a good start! Remember to document at least with comments lang!
If not, just remember to comment your lines.
I'm saying this because on that situation, you have to be really flexible. If the project doesn't get finished before your OJT ends, then at least you have a good amount of comments/documentation for the succeeding analysts and programmers to work on.
I've had clients like this and the only thing I wanted to do is to punch them in the face or screw them over. But seriously, no project takes a lot of time basta programmer magbuot. It's the client that screws you, a lot. This comic should give you more insight about it:
How a Web Design Goes Straight to Hell - The Oatmeal