Yes, that will do exactly as you've stated. This is where you can try it yourself in a simple test case:

while ( chomp($_ = <DATA>) ) {
    print /^((\d+)\-(\d+)\-(\d+)\s+(\d+):(\d+):(\d+))/ ?
        "Matched on '$_': $1\n" : "Unmatched on '$_'\n";
}
__END__
1990-01-01 00:00:00.000
1990-01-01 00:00:00.000
1991-08-06 12:21:12
1991-08-07 13:41:15.65
1992-09-2110:10:10.100
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