It's nice to hear from you again!
First of all, concerning tax report there are two types of people: 1) those that have to do a tax report and 2) those that can do it if they want to. I'll provide a short overview of what to keep in mind for both groups:
1) As far as I can see the deadline for tax report of 2016 was 27 March 2017. But if you are doing the report with a tax accountant the deadline will be prolonged until 31 December 2017 automatically.
You can apply for extension, but as far as I can see you have to do that before the deadline.
Even though it is mandatory to do a tax report, there are millions of employees that don't hand it in. Be careful with that because not only are you missing out on possible refund, but the tax office might ask for tax reports retroactively.
2) You don't have to do tax report...
- ...if you are single
- ...if you only work for one employer
- ...if you are not working self-employed
- ...if you don't get income from renting (or if this income is lower than 410€ per year)
- ...and if you are not getting benefits (e.g. unemployment benefits, parents' money or sickness benefit) or if those benefits are less than 410€ in total per year.
Yet still it can be a good idea to hand it in since you can get a refund.
If you are not obliged to to a tax report you can take your time: you got 4 years to do the Steuererklärung.
Sources (German language):
I hope this answer was helpful to you. If anything remained unclear: just ask!