as far as I know it is not possible to create activity in PJL which last less than 24 hours Therefore it is not possible to create several activities with predecessor which must start the same day but at different time.
Activity 1 start at 9am
Acitivity 2 start same day but only when Activity 1 is completed.
I believe it would be good to have the possibility to control the time. Per default PJL could still assume that activity will last more than a day but if needed the user can set different duration less than a day.