He's in the normal timeline right now. Here's when recent non-incumbent Presidents have picked their running mate recently:
2016: Trump July 14, Clinton July 22
2012: Romney August 11
2008: McCain August 29, Obama August 23
2004: Kerry July 6
2000: Gore August 8, Bush July 25
1996: Dole August 10
1992: Clinton July 9
1988: Bush August 16, Dukakis July 12
1984: Mondale July 12
1980: Reagan July 16
So, as we sit here on Aug. 5, 2020, in the last 40 years of non-incumbent candidacy, the candidate has named VP by now in 8 of 14 cases. This is hardly "concerning".