Should I inform my thesis adviser about current situation I had unofficially agreed to start working on my thesis during September, with no concrete date being mentioned.

However there are two factors which might delay this date:


Me not being available due to travelling until the end of the month
I don't feel confident about the programming task that has to be done during the thesis, so I want to take a little bit more time to work on some exercises


The problem is that in case that I go there, they might request me to sign for the official thesis registration, which then will impose the deadline when I have to be completely done with all the thesis stuff. I don't want to do this, before being confident that I can proceed easily with the programming, because otherwise the period that I will spend doing some extra programming exercises will be eating from timeslot limited with the deadline.

My question is, should I inform the adviser about these developments, or should I shut up until I come back (and use another 10 days to do some extra exercises) and then go to his office and talk about the official thesis start?
Which situation would reflect best on me? I'm afraid I am causing too much communication overhead unnecessarily and somehow not respecting the time-frames I have agreed myself.

Reason to go to the advisor: I have already verbally promised that I will be around once September comes

Reason not to go: They may require me to sign the official thesis start.
As a rule of thumb, if you tell someone you'll be doing stuff with them at time X, and then change your mind, let them know!

More specifically, I would recommend an email such as:

"Dear Advisor,

we had planned for me to start my thesis in September, but because of REASONS I'll only be able to start on October. I apologize bla bla
In the meantime, I'm planning to do EXERCISES. Please let me know if you have any other suggestions on how to prepare."

I don't see a point in telling this to your advisor in person anyway, and this should keep you safe from being made to sign stuff.