To our knowledge, the closest mikveh to the Inbal is at Rehov Ha'Ari, number five. Their phone number is 02-563-2783. We spoke to the balanit there tonight. She said that the mikveh will operate Seder night on a Shabbat schedule. We suggest calling a night or two before to verify exact times.
On seder night, much as for a Shabbat immersion, you will complete most of your preparations prior to candle-lighting. This mikveh is about a 15 minute walk to the hotel (go up Jabotinsky until the President's house and look on your right for the beginning of Rechov Haari – the mikveh is down that block on the right) We suggest scouting out the walk prior to Yom Tov so that you can get there without trouble. Thus, the time spent at the mikveh should not be too great and it should be possible for the whole process (including walks to and fro) to go quickly, in which case we think you could safely arrive in time for seder or even to meet your husband at shul. This case does not allow for immersion during the day (any more than a typical erev Shabbat would). If, however, you cannot work out the logistics, you could delay the immersion to the following night as a last resort.