I'm assuming the purpose of the module is only to calculate the eta, and not to generate and update the web page (otherwise a name like Time::ETA::HTML would be more appropriate). So yes, certainly complete and upload it if you cannot find a module to fit your needs. But please:

• design a reasonably intuitive api
• document it clearly
• include "see also" in the POD with a list of similar modules, such as Term::ProgressBar
• be willing to do the necessary maintenance