It looks like a good offer. It should be done wbefore April, especially if you ask Jarvis to "pull out all the stops" (hurry). You cannot demand that it be dealt with by a certain date, but you could mention that the monies might no longer be available after April 1st.
I would hope that the offer will be accepted, but, if not, then the IVA could fail if you cannot continue paying from Hungary. Now that the UK is no longer in the EU I do not know what, if anything, British based creditors can do to chase the debt --- some UK creditors might have EU based offices that could chase the debt through European Courts and enforcement systems.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014