Lead Time in Project

[Rebel.Ranter]

Is a lead time mandatory or optional?

I have two tasks that have a *finish to finish* dependency with a lead
time of 2 days

Task A duration 8 days
Task B duration 10 days
The lead time is 2 days between A & B

My question is this, when I specify the lead time am I saying?:

(a) B *must* finish 2 days before A at all times, i.e. a mandatory gap
of 2 days is required.
or
(b) B can finish 0-2 days before A, i.e. 2 days, 1 days, or same day

Thanks in advance for your help on this, putting it into MS Project
doesn't make it clear to me, maybe it's just the way I am entering it.

 

[Dave]

B will finish at least 2 days after A.

 

[Rebel.Ranter]

B will finish at least 2 days after A.

But it is a lead not a lag so B would finish before A surely?

 

[Dave]

But it is a lead not a lag so B would finish before A surely?

If you connect A to B F-F then the finish of A drives the finish of B.
So, the later that A finishes, the later it is that it pushes out the
finish of B.

 

[Rebel.Ranter]

Thanks Trevor, Imust confess that I am an engineer doing a business
degree at night. This question stems from an assignment we were given on
AON network diagrams (forward path, reverse path, early finish, late
finish, etc.)
I think represents bad planning but the lecturer wants us to understand
the principle of finish to finish relationships & aslo leads (-ve lag).
I don't believe that she should have asked the two together in this way,
while you may be able to get to theory to work out I don't think
real-world tasks could achieve this type of timeline.
Thanks for the response.
Regards,
Mark

 

[Rebel.Ranter]

Also thanks to Dave for your response.

 

[Steve House]

When scheduling from start forward, links set the earliest date the
successor start, or finish, can happen. It may always happen later. So
you're saying "B can finish no earlier than 2 days before A finishes." B
might finish any time after that but it can be declared "done" no earlier
than that. So it's not "B must finsh two days before A finishes," it's "B
can finish no earlier than 2 days before A finishes."

I'd be very cautious about using such constructs in a project plan because
it really requires clairvoyance and that is in short supply these days - it
requires you to know with absolute certainty when A will finish 2 days
before it actually finishes. What happens if the resource working on A
calls in sick the day before you though it was going to be finished? What
do you do about B now?