returns number of blank cells between values

So row 3 is in fact completely blank...

The prior formula for B1 does what you want you just need to change the reference to B3 to be B4 - ie the first days records.

EDIT: scrap that - no it doesn't - you need to change ISNUMBER test - revised below

If you're inserting rows such that you can't use the reference B4 (ie will become B5 when a new row is physically inserted) then use INDEX instead, ie:

B1:
=LOOKUP(10^10,CHOOSE({1,2},COUNT($A:$A),MATCH(TRUE,INDEX(INDEX(B:B,4):INDEX(B:B,MATCH(10^10,$A:$A))<>"",0),0)-1))

else if you prefer to keep B3 then subtract 2 rather than 1 from the result (to account for row 3 being ineligible)