Yes, it helps. In fact, if you'd said it in your first post then we could have possibly saved many posts.
The simple capacitor circuit that evaded Maestro Searcher Eclectic won't provide that for you. However, it may be good enough. Especially as you haven't indicated the 'pre-determined' length - so we're back to guessing.
If you want accuracy and reproducibility you need to look at something like an edge triggered monostable. There are numerous ways to achieve this so get Googling. You can do it with discretes or chip plus bits.
But, that simple cap input may be good enough. Do you understand how it works?
Incidentally, that circuit plus a 555 can do it.
And, it really helps to have a 'scope when experimenting so you can see what's going on.
And then Nick can see what the diode does