exclude module from timing synthesis

Why do you believe the first one does not work? Any easy test is to run report_timing on a path from that hierarchy and see if it gets reported. If it works, no paths should exist(although they will show up if you add -false_path to your report_timing command)

Note that get_pins finds the inputs/outputs on every cell, where really you don't need to apply it to combinatorially cells or anything like that. You might just do:

set_false_path -from [get_keepers {inst0|inst1|*}

The -to is unnecessary since you just want everything. Also know that get_keepers will use the longer naming style of |entity:instance|entity:instance|... so you need to accomodate that. Just run this directly in TimeQuest first and see if it takes and makes the paths disappear. Once you're sure it's working, add the constraint to your .sdc and compile.