Electronic – Wide voltage supply for PIC microcontroller

What is REALLY important is to have 0.01-1uF ceramic capacitor soldered right on the power pins of every digital IC in your circuit no matter what is the power source.

So I belive even your current PSU will be fine if you add ceramic caps where needed. Linear regulators provide very stable power, so you should be good with what you have now (unless it is oscilating - might happen if ESR of caps does not match regulator requirements - usually happens on LDO regulators rarely).

In my projects I use USB as my main power source. It gives you stable 5v and it does have current limiter.

You can ether get it from your PC(should be careful a little) or from tiny mains adaptors which have USB output.

Then you use your linear regulator if you need less then 5V.

How accurate does this 30 day period have to be? 30 days is about 2.5 million seconds, with a crystal accuracy of 20 ppm you might have a one minute error after 1 month.

If a one minute error is unacceptable you could use a temperature controlled oscillator or a better crystal, like 5 ppm. If external aid is allowed you could use the signal of a DCF77 receiver (Europe, WWVB for North-America). These will give you a tick per second with atomic clock precision. All you have to do is count pulses. Note that DCF77 has only 59 pulses per minute, the omitted pulse indicates the start of a new minute. If you take this into account your 30 day period has elapsed after 2 548 800 pulses (59 \$\times\$ 60 \$\times\$ 24 \$\times\$ 30).

If the PIC has to do it all by itself that shouldn't be a problem either. Clock at 32768 Hz and program a timer to give an interrupt after 32768 clock cycles, that's one second. Count 2 592 000 interrupts (60 \$\times\$ 60 \$\times\$ 24 \$\times\$ 30).

In a month a lot can happen, and you probably want a battery backup in case there's a power outage. If you use the atomic clock signal you can also decode the time code after each minute pulse and compare date and time with your target time. In that case power outages don't even matter.

edit
You don't mention which PIC you're using, and without any practical experience with them I know there is a lot of them. I'll pick the PIC10F200 because as I understand it it's (one of the) least capable PICs, just having one 8-bit timer/counter.
The timer/counter can be clocked internally by the clock/4, and has a selectable prescaler. If you use a 32.768 kHz crystal for the clock, then clock/4 = 8192 Hz. Set the prescaler to \$\div\$32 and the 8-bit timer/counter will overflow once every second.

edit 2 (re Olin's comment)
Olin points out that the PIC10F200 only has an internal oscillator. That won't have crystal accuracy, but you can clock the timer from an external clock. Connect the output of the 32.768 kHz oscillator to the T0CKI input and set the prescaler to \$\div\$128. Then the 8-bit timer/counter will overflow once every second. As I understand it there's no overflow interrupt, so you'll have to detect this by comparing the timer value to 0x00.

edit 3 (re your comment on accuracy)
Allowing a two day error in one month is what we call very low accuracy. That 6.7%. The internal oscillator is calibrated to 1% at 25°C, 2% over the full range. So if you want you can use the internal oscillator, then you don't need the external 32.768kHz crystal. The oscillator is tuned to 4MHz, \$\div\$4 gives you 1MHz at the timer's prescaler. If you set the prescaler to \$\div\$64 then the 8-bit timer is clocked at 15625Hz. Count 61 overflows for every second, even if you ignore the remainder you still get 0.06% accuracy.