Yes, you can. You will establish a finish to start relationship first, then
add a lag amount to force a delay. First, you will need to link your two
tasks together, task 1 and 2. Go to the task information dialogue box for
task two, then the predecessors tab. You will see task 1 listed. You will
also see a field called lag. Enter 20 days. This means upon the completion
of task 1, 20 working days later, you will begin task 2.
This is the short answer. Remember to use a FS relationship; lead/lag is
all based on your working calendar.
I hope this helps.