How to Estimate Times for Projects in a Programming Workshop?
Test drive

Grab a couple of local students of comparable level and have them do the assignments.

Your own speed is not indicative - something that takes you five minutes may take ten minutes or may be incomplete after an hour; only practical experience can show how it will turn out.

In addition, usually setting up a working development environment can be a major time sink - if people use their own hardware and various operating systems, then some of them can waste a lot of time until they are able to run a 'hello world' program; you should have a clear plan on how you will handle it.