quorthon is right that you can't start your rehab straight away, because the risk of rupture is quite high. Hopefully you didn't think I telling you to start doing those things. At 6 weeks your surgeon will decide wether to refer you to physio.
This is just your first injection? if it is then thats good - surgeons tend not to give more than 3 for fear of really breaking down the tendons and causing the to become structurally impaired.
If you aren't able to take it easy at work then you may have to take time off... the risk of rupture can be high in that first 6 weeks (hense why your in the boot)