When both husband and wife agree, mikveh immersion may be delayed. If you both consider immersion under the circumstances you describe too difficult, then you may immerse after Yom Tov.

Please note, however, that the seder usually begins well after nightfall, and everyone arrives home later than on a regular Friday night. With a little help, you may well be able to immerse without causing any real delay. Telling another female family member about your immersion is permissible if it will make it easier for you to go out and return discreetly.

Chag kasher vesameach!