Some of the SAM Brass uses ADSR.  Some of the new "Garritan Orchestral" strings use an ADSR style instrument design.

In the example of wood wind instruments, I'm afraid your only options to adjust the the 'release' time is to somehow change when the MIDI note Off event occurs, and/or make adjustments to the reverb send control (CC91) for the channel.

GPO5 does NOT respond to 'note off velocity', nor do any of the instruments include sampled and triggered 'reverb tails' (it's a very dry approach, any reverb you get is going to be done with the reverb effect units).  So if you want ramps, curves, or other envelopes done to the sustained dynamics over time (I.E. to make a flute fade a bit on note release', then you'd need to draw in a CC1 curve for that decrescendo type of effect.

If you're working with a track style DAW, adjust Note velocity, CC1 expression volume, and of course, the actual length of the note (where the note off event occurs) to alter the attack, release, and timber of notes.  It's fairly easy to achieve in a standard piano scroll type MIDI editor.

If you are working with a Scoring style application like Finale, Sibelius, or Dorico, then these fine adjustments are often possible, but a bit more involved to control on an individual note by note basis.

Examples:

In Finale and Sibelius, sometimes changing the 'groove' style can make a big impact.  Each groove can have adjustments on the true duration of each note type.  I.E.  Quarter notes should get 100% duration, or 90%, or 110% (for legato overhang), and so on.

Finale and Sibelius also have various options to control the actual real time velocity and duration of individual notes.  I.E.  Change a note's attack velocity and make it it play only 97% of the full note duration.  I.E.  Select a range of notes, and extend all of their duration by x number of MIDI ticks, and so on.

It's also possible, though not trivial to make use of the sample content that comes with GPO and craft your own 'instruments' using that material.  For instance, one could start with a flute sfz file in GPO, and make tweaks to fundamentally change how it plays back the samples (Dynamic shaping envelopes, user applicable responses to CC events, etc).  For all that trouble however, I personally would rather simply move the work into a Tracking DAW where I can easily fine tune note releases and like using simple batch editors and the like.

One of the great things about GPO 5 is that it's inexpensive, and rather small (system resource layout required), and runs super lean.  Unfortunately, this also means we as users must learn to 'control' the library in ways that can milk the sounds for all they are worth.  That requires more direct user intervention along the time-line of our playing 'sequence'.