Sum times with NULL values in time end field

I have 2 rows in my SQL 2008 db with these 3 columns 

Name | Time_In | Time_Out

Here are the 2 rows

Jim |  2013-05-08 07:00:00.000 | NULL

Pat |  2013-05-08 06:00:00.000 | NULL

Now I want to calculate the SUM in minutes of the time differnces between NOW and the Time_In  ------for both Jim and Pat

Example , Lets say its 10:00 now.

That means that Jim has 180 minutes  Now (10:00)  - Time In (07:00:00.000)

That means that Pat has 240 minutes  Now (10:00)  - Time In (06:00:00.000)

SO the totals for Jim and Pat are 420 minutes. Thats the number I want.

I started using SELECT  SUM(ISNULL(Time Out,NOW)) AS  minutes_worked ................

But Im not sure thats the best way to do this.

Any ideas?