Many things factor into it.. Heres the basic factors
- The type of script
- The persons ability
- The persons laziness
If it's a simply mod script (Like removing the Save) it should only take less than five minutes, however if it's remaking the whole Menu system it may take a couple hours. Especially with the whole "Trial and Error" type thing.
If the person knows alot about Ruby it shouldn't be very difficult, but if they don't know that much. The may encounter and error they have no knowledge about fixing.
If the person is lazy they may just do a couple of lines and work on it in the next day or two. They may even forget about it complretely. So sometimes it's best to remember.
There that should be an accurate, quick summary about it.