What??? Such an assumption is known as an "unsound extrapolation of data". It assumes that because a little bit of change can occur over a short time then that trend can continue indefinitely, producing massive change.
Example: The stock market drops 110 points in a day. Based on that change, in three months time the value of all companies on the DOW will be zero.
Example: The temperature at 7 AM was 35 degrees F. At 2PM it was 60 degrees. In another three days it should be hot enough to boil water.
Example: I decide to get myself in shape and start jogging, timing myself once a week. THe first time it takes me 7 minutes to jog a mile. Next week its down to 6, the next down to 5 min, 20 seconds. How long will it be before I can run a four minute mile?
All of these examples demonstrate an unsound extrapolation of data, as does your mircoevolution + time = macroevolution assumption.
MANY things in nature are a WAVE FORM, they change, but it is change around a mean. THey can only go so far from the mean of the wave form. Your micro + time = macro assertion is unwarranted, as there are too many other reasonable possibilities.
Name two.