The important thing regarding SIC time and the ATP certificate, is that ALL SIC time counts towards the 1500 TT as long as the airplane requires two pilots and it was conducted under 121 or 135 ops.
Here is a link to the FAA examiners manual which puts the regs into more easily understood language:
http://www.faa.gov/library/manuals/e...5/5_002_01.pdf
A. Total Pilot Flight Hours. A minimum of 1,500
total pilot flight hours must have been accumulated by
the applicant. The following types of flight experience
may be credited toward the total pilot flight hour
requirement:
• All pilot-in-command (PIC) hours
• All dual instruction received by the applicant
• All flight time acquired as a second-in-command
(SIC) in aircraft requiring at least two pilots by
the approved airplane flight manual (AFM), airworthiness
certificate, or in FAR Part 121 or 135
operations
• For commercial pilots, up to 500 hours of flight
engineer (FE) time acquired in FAR Part 121
operations (The FE time must have been
acquired in an airplane requiring an FE. While
acquiring these hours, the applicant must have
held a commercial pilot certificate and been participating
as a pilot or FE in a FAR Part 121
approved pilot training program. FE time may be
credited at a rate of 1 hour of pilot time for each 3
hours of FE time. For example, if the applicant
has accumulated 300 hours of FE time, 100 hours
may be credited toward the 1,500 total pilot hour
requirement.)
B. Hours as PIC. The applicant must have accumulated
at least 250 hours an PIC. SIC hours acquired while
performing the duties of PIC under the supervision of a
qualified PIC may be credited toward this requirement.
C. Hours of Cross-Country. At least 500 flight hours
must have been accumulated as a pilot in cross-country
flight. Cross-country time is that time acquired during
flight from a departure point to a destination point that is
not the same as the departure point. It is also time
acquired in a flight that is cross-country in nature even
though the departure and destination points are the same
(such as forestry patrol).
D. Hours of PIC Cross-Country. At least 100 flight
hours must have been accumulated as PIC while conducting
cross-country flight. SIC hours while performing the
duties of PIC under the supervision of a qualified PIC
may be credited toward this requirement.
E. Hours at Night. At least 100 hours must have been
accumulated as a pilot at night. An applicant who has
made over 20 night landings may thereafter substitute one
additional night takeoff and landing to a full stop for 1
hour of nighttime.
F. Hours as PIC at Night. At least 25 hours must have
been accumulated as a PIC at night. SIC hours while performing
the duties of PIC under the supervision of a qualified
PIC may be credited toward this requirement.
G. Instrument Hours. At least 75 hours must have
been accumulated as a pilot in actual or simulated instrument
conditions. Fifty hours of this time must have been
in actual flight