Probably timed just to try and scuttle Trump's meeting with Putin, don't think it will work because I don't think either Trump or Putin give much of damn what Mueller does anymore.
Believe it or not, I don't think the timing of this announcement has anything to do with Trump.
It has everything to do with yesterday's revelation that Clinton's e-mails ended up in the hands of a foreign government. They have to maintain the fiction that this all someone else's fault, not hers.