Do not worry about the 45 days. Hindi sila ganun kahigpit. When you submit your docs, maglagay ka ng cover/transmittal letter at dun mo banggitin kung kailan mo natanggap. something like this:
In compliance with your requirements in your letter dated ___________, which I only received on ______, I respectfully submit herewith the following documents:
1
2
3 etc....
Advise ko wag ka na gumawa ng separate letter na hindi kasabay ng docs dahil baka makadelay pa. Just make sure you submit within reasonable time (say within 2 weeks). Kung matatagalan ka sa pagproduce ng docs, then you may write asking for extension. Magbigay ka ng approx date kung kailan mo maipapadala.
Hindi rin naman nila sure pa kung nasan ang delay, baka sa pagdeliver ng docs mo papunta sa kanila. Kaya nga di ka nila pede basta na lang iforfeit kung lumampas na ang 45 days.