Well, the first pointer is that ONLY YOU can know how long something will
take.
The #1 mistake that people make is to accept some other persons estimate of
the time involved. So, if you hire a few software developers, then THEY must
make the estimates of how long it will take to build something..not you!
Since YOU are the one building this, then ONLY YOU can make a estimate as
to how long a task will take. My estimates are of no use to you, since on a
developer team, the rate of development often varies by a factor 10, or even
MORE. That means in two days of my work, it will take you 20 days (assume in
am 10 times more producing then you). And, that would mean that 3 days for
me will equal 30 days of work.
These kinds of differences are NOT normal for most industry's. So, while
someone in your lab can normally weight out some samples for measuring
Microbial metabolism in soil, the time taken to do this might be a factor of
2 times slower for a new persons vs an experience person. But, in software,
factors of 10, or even 100 time are common place. Some developers actually
CODE in excess of 1000 lines in one day.
However, here are some pointers:
You can't make a estimate of the application until you actually design
it. Do you have 5 forms, or 50 forms? So, while it sounds silly, but to get
a real accurate estimate, you need to actually design the application. And,
BEFORE you design the application, you should build or make what is called a
functional spec. You can find info on how to do this here:
http://www.joelonsoftware.com/articles/fog0000000036.html
And, here is a good article on make a good user interface:
http://www.joelonsoftware.com/uibook/chapters/fog0000000057.html