...I'm a little confused about the Oct 15th deadline. So I can contribute to a tIRA up until April 15, then if I need to recharacterize into Roth, I have until Oct 15 to do that?
Sort of.
A contribution to an IRA is deemed to have made on the last day of the preceding taxable year "if the contribution is made on account of such taxable year and is made not later than the time prescribed by law for filing the return for such taxable year (not including extensions thereof)". 26 USC § 219(f)(3). If your taxable year is the calendar year, then the deadline to contribute to an IRA for 2015 is April 15, 2016. 26 USC § 6072(a).
The deadline for making "adjustments" to contributions (what the IRS and posters here call "recharacterisations") is different. The adjustment must be effected on or before "the date prescribed by law (including extensions of time) for filing the taxpayer's return for such taxable year". 26 USC §§ 408A(d)(6)(A), (d)(7). If your calendar year is the taxable year, the maximum extension of time in most (but not all) cases is an extension until October 15. 26 USC § 6081(a). However, in order to benefit from such an extension of time, it actually has to be granted to you. Subject to certain conditions, you can obtain an extension until October 15th by filing Form 4868. 26 CFR 1.6081-4(b). You could file that form now to secure yourself the benefit of the extension.
If you elect not to file Form 4868 or otherwise obtain an extension, then the deadline for recharacterisations (assuming your taxable year is the calendar year) is only April 15th. However, the Secretary of the Treasury has generously promulgated a regulation authorising retroactive extensions of the deadline, subject to conditions. Specifically, you can obtain an extension until October 15th (even if you failed to ask for one originally) if you, among other conditions, (a) timely filed your original return and (b) comply with certain procedural requirements including writing "FILED PURSUANT TO § 301.9100-2" on top of the amended return that you file to effect the retroactive extension. 26 CFR 301.9100-2(b), (c), (d).
If you want to keep things simple, you can file Form 4868 and that will lock in October 15th as being the deadline (subject to the fact that the Secretary retains the authority to revoke an extension on 10 days' notice: 26 CFR 1.6081-4(d)). If you fail to file Form 4868, you may not be able to recharacterise after April 15th without filing an amended return to request a retroactive extension pursuant to 26 CFR 301.9100-2, even though Roth contributions are normally not reported on returns.
The IRS has also discussed the above points in Publication 590-A under the heading "
Extension". Please note that, like all secondary sources, IRS publications "do not have the force of statutory enactment nor do they supersede judicial decisions".
Schott, Inc. v. Kalar, 20 CalApp4th 943 n 4 (CA Ct App 1993). That is also true of my posts.