I can safely say No, it shouldn't make you're buzz any less noticeable.
I myself, as a person who uses opiates almost exclusively for productivity and work purposes, I like to have all of the little things like showers done BEFORE I actually dose. That way I have 4-6 hours of uninterrupted time where I can be productive in whatever way I choose.
So my typical evening schedule goes like this..at about 10pm this starts a little like this; 1.) Shower 2.) Brush teeth 3.) Take Adderall(sometimes, mostly after long days) 4.) Tune guitars 5.) Make a song list to save time 6.) Make tea 7.) Repeat#4, and last but not least number 8.) Take my opiates of choice in my dose of choice....Relax with hot tea, music for the first 30 minute come-up (the best part) then after 30-45 mins of chilling and feeling good i'll get up and start doin my thang, ya dig?
This way, I don't have to worry about any little interruptions or nussiances that may arise. Sometimes you ignore you're environment until you take your dope & start to feel better...then notice your house is a mess, lol. I hate that....so I clean the house up, have everything I need for a good, smooth running, good-timin' night of chill productivity.
THAT WAY, I don't blow my buzz by getting angry and all bent out of shape because X little easy-peasy every day activity is taking me forever, or otherwise just in my way, frustrating me, or all around fucking with my good vibe.
That's why, for me, it's essential for me to have everything in order, BEFORE I do drugs...
Methadone isn't very special anywho, so I say go ahead and take that shower...