Am I correct?:

A non-exempt employee is paid travel from the house to the hotel. An employee departed their house from the east coast at midnight (our time/west coast) travelled for 27 hours. The way I figure it is they recieve 8 hours of regular time, 4 of OT, and 12 hours of DT.

the remaining 2.5 hours is attached to the 4 hours they worked the afternoon of arrival, for a total of 6.5 regular hours,

Yes? or No?

Unless you are in California, there is no legal requirement to pay double time.

If that is your company policy, abide by it.

We are in Ca.

I guess my question is really about the 2.5 hours after midnight that goes into the next day. Is that paid out as DT because it was part of the travel from the previous day, or paid out as regular time and attached to the 4 hours they came in for processing.

You have several different rather unrelated issues that are being jumbled together.
1. Figure out what hours worked are. Under federal rules, this is covered by the regulations 29 CFR 785.33-785.41, but the general rule under federal regulations is that Non-Exempt employees are paid travel for traveling during their normal worktime (8-5 for example on any day of the week including weekends and holidays). However there are exceptions so everything in that group of regulations really needs to be read. Federal travel regulations. (http://www.dol.gov/dol/allcfr/ESA/Title_29/Part_785/29CFR785.33.htm)
2. CA rules in this area are a little different then federal. Both federal and CA travel rules need to be looked at.
http://www.dir.ca.gov/dlse/DLSEManual/dlse_enfcmanual.pdf
46.3 Extended Travel Time. The California rule requires wages to be paid for all hours the employee is engaged in travel. The state law definition of “hours worked” does not distinguish between hours worked during “normal” working hours or hours worked outside “normal” working hours, nor does it distinguish between hours worked in connection with an overnight out-of-town assignment or hours worked in connection with a one-day out-of-town assignment. These distinctions, and the treatment of some of this time as non-compensable, are purely creatures of the federal regulations, and are inconsistent with state law. (O.L. 2002.02.21).
3. Once hours worked is determined by looking at both federal and CA rules, then the CA OT rules (http://www.dir.ca.gov/dlse/FAQ_Overtime.htm) need to be looked at.
4. Lastly, like Scott says if the company has a policy/contract/CBA more generous then required by law, then so be it. But be very clear what the law(s) actually says, because policies/contracts/CBAs cannot make the law(s) go away.