SourceTree 1.8.2.11 on Win10
Repository and destination are both CentOS systems.
After initiating a clone it seems to take a while (not measured) until the new clone directory is created and .git directory is created and populated. Then there is a crazy delay of some 13 minutes until the very first repository file is cloned! At the command line it is such a short time it can't even be reasonably measured.
There are over 14,000 file sin this repo. Perhaps SourceTree must know of all of them prior to the first clone. Just hypothesizing - I have no idea, yet this needs an answer prior to us completing our evaluation.