I wish you didn't feel defeated. This is really high potential lyric.
Here are a few suggestions. Feel free to use, or not use them as you think is best.
envious time
fly, fly, envious time
until thy race is run out I don't think you need this. The near rhyme with "now" isn't necessary to my ear.
leaden-stepped feet will not compete
accept defeat just for now
fortuitous surprise has unlocksed my mind
fly, envious time
fly, envious time
sleep, sleep, desperate need
smother me, safe from all harm
oblivious friend will know me then
release me when all is calm
if I die before I wake, pray the Lord, my soul to take
fly, envious time
and please don't leave me behind, envious time
I do only improve
with things t'which I am inclined
new moon, both eyes on you
surrender to any virtue of mine
a little worse for wear
n' too far gone to care
fly, envious time
and please don't leave me behind, envious time
envious time
Notice no "additions". . . only subtractions. And it could be that your rhythm requires those syllables. I just felt it flowed better without them. But again, I don't know how you will sing this.