Yes I suggest you use a pot on the final unit so you can adjust the time from say 2 secs to 20 secs, so you can use the unit on most installations.
Also I'd suggest that you include some sort of interlock within the software so that both star and delta contactors dont come in at the smae time and atke out the supply (Ok they are not going to pull in at the same time, but for some reason if one jams in then the micro should pick that up and prevent pulling another in causing a short, this is usually done both electrically and mechanically with commercial starters).