Hi @Home and a warm welcome to the Community Forum and congratulations for being accepted for your first sit! 
In answer to your question, this can vary from literally a few minutes which has happened to us in the past to hours, days, weeks. The longest we have waited was around 8 weeks.
For reference as a member, you can also add your TrustedHousesitters profile on to your Forum profile by following the attached link, should you wish. This will then enable others to offer you helpful advice and feedback.
If you are unsure how to do this, or if you have any questions at all, do not hesitate to ask, we are all more than happy to help.
Also, remember you can use the spyglass symbol at the top of the page next to the TrustedHousesitters logo and search for any questions that you may have as they have most likely already been answered on here and of course if not then please just ask!
I have attached a thread below, it would be great if you could join in with this as we think you could offer great feedback and your input would be a great addition 