Yes, it is applicable to Humility, but not in that case. Because timestamp effects only apply if two effects are on same layer. Let's assume another card makes all creatures 5/5 instead of 1/1, if that card came into battlefield first and then Humility, creatures would be effected by Humility because of timestamp and become 1/1.
And vice versa, they'll be 5/5.
Also you can check Deathless Angel's ruling for this purpose;
"Deathless Angel's ability doesn't grant an ability to the targeted creature. Rather, it affects the game rules and states something that's now true about that creature. The creature will remain indestructible for the rest of the turn even if it loses all abilities."
I'm a judge myself and I'm pretty sure that works that way.