Liturgy for Yoma 175:7

וקי"ל דבטבילה בזמנה מצוה פליגי

This implies that R'Jose would not hold this not to be obligatory, but surely it was taught: If he has had the name [of God] inscribed on his body he must not bathe, nor anoint himself, nor stand in an unclean place; if it happens that he is obliged to immerse himself, he should tie some reed around, go down and immerse himself, R'Jose said: He may go down and immerse himself in the usual manner, provided he does not rub it off. And we know that they are disputing the principle as to whether it is obligatory to take the ritual bath at its definite time!<span class="x" onmousemove="('comment',' V. supra 8a.');">⁸</span>

Hadran