いまいった in the above sentence can be analyzed at least in two ways. The first is much more probable than the second in any context.
いま (now) + いった (have said) meaning, as I have said
いま (now) + いった (have passed away)
Considering the context and a very particular adjective of すじのいい (natural bent), it will be safe for me to determine on the first analysis. ...
This ところ refers to a particular situation/scene, and ～ところを is a set phrase that means (本当は)～ところで or (普段/本来は)～なのに. See: Does ところを always mean the same thing as のに? What is the difference between ところへ and ところに?
4分のところ is a somewhat abbreviated expression, but it means 通常は4分のところ or 本来は4分待つところ, or "the situation where one normally waits for 4 minutes". ...
Different kanji allow for nuance, but also can be used to give a literary flare.
According to my 漢和中辞典, 滲みる describes water deeply soaking into something. 染みる describes something slowly soaking through something else.
The nuance here seems rather subtle, but given what you've said, if it's just a matter of something ...