What is the acceptable upper limit of time allocated to a single development task?

Question

When asked to estimate and/or while reading my coworkers estimates they often read something like this:

1. Make new ############# page with feature ############## - 8 hours
2. Create new ########## control - 21 hours
3. Solve bug in ######## module - 15 hours

I think that when the estimate for a single task is more than 5 hours you should strongly consider dividing the task up into smaller sub-tasks.

The problem with estimates like 21 hours is that you risk losing a lot of hours without management ever knowing about it until it's too late. Also, large estimates can be an indication that the task is poorly defined. Of course this can't be a very strict rule since it is easy to conceive exceptions to it.

So my questions are:

1. Do you have an upper limit for your task estimates, and if yes where is your limit?
2. What is an acceptable level of detail for a task in your opinion?

Answer 1

When we do our planning, we break things up into 4 hour tasks (at the longest). And, we only plan for 4 work days per week. (We figure that the rest of the time is taken up with meetings, etc.)