Countrows help

Not sure how/if it can be done with a DAX measure, however here is a formula based proposal.
Populate a column of discrete hours 0:00 ... 23:00
The adjacent column is populated using:

Formula:

=SUM(SUMPRODUCT((MOD(Table1[Arrival],1)>=I2)*(MOD(Table1[Arrival],1)<SUM(I2,1/24))),SUMPRODUCT((MOD(Table1[Exit],1)>=I2)*(MOD(Table1[Exit],1)<SUM(I2,1/24))),SUMPRODUCT((MOD(Table1[Arrival],1)<I2)*(MOD(Table1[Exit],1)>=SUM(I2,1/24))),SUMPRODUCT((INT(Table1[Arrival])<INT(Table1[Exit]))*(MOD(Table1[Exit],1)>=I2)))-SUMPRODUCT((INT(Table1[Arrival])<INT(Table1[Exit]))*(MOD(Table1[Exit],1)>=I2)*(MOD(Table1[Exit],1)>=I2)*(MOD(Table1[Exit],1)<SUM(I2,1/24)))

Let us know if you have any questions.