Exactly. I found this on a fact sheet a few years ago:

"Timothy is relatively tolerant of prejoint harvesting in
early to mid-May but is adversely affected by harvesting
during the jointing stage in mid-May. In addition,
harvesting at early heading reduces yields and persistence,
compared with harvesting at either early or late bloom
(Table 3). Harvesting the spring growth of timothy at early
heading reduces first harvest yields, and there is generally
no increase in yield of subsequent harvests to compensate
for this loss."

Go to timothy#24.    Click on the PDF file.