As he waits for the party to approach, Ilnesh searches the door thoroughly for traps.
Should they round the corner before he is done, he will simply swing the doors open to hide the text on them from Timeon.
Spoiler: OOC
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That's taking 20 on a search, if it's less than two minutes (which I expect it will) till the party gets here, just a roll and opening the door. Preemptive perception roll: (1d20+3)[12]