Well 90 days from dec 10 is actually March 10. The normal percentage completion rate for the full 90 days is 1.1% a day. So 90 * 1.1% is roughly 100% completion.
So if 75% done on Jan 21, which is the 42 days. 42 * 1.1= 46% where they should have been at the normal rate.
They are going at a current rate of 1.8% a day, which would mean they reach 100% at around 55 days.
55 days plus the original dec 10 date is Feb 3.
This is all speculative on what they would consider as 75% complete.