O PC, why are you so slow?
def get_range_list(amount, val, end):
    return [
        ('flcon1:DataValue~Osiris_Test_Data_' + str(i + 1) + end, randint(0, val))
        for i in range(amount)
    ]


You're only interested in the value of amount, not in the variable it produces itself. Have you tried using xrange instead? xrange is much faster than range.

Afar from that, I cut-out the OPC parts and ran the rest through a profiler.

python -m cProfile -s tottime CR_135184.py 1000000 1


Cut code:

import argparse
import sys
import time
from random import randint

def get_args():
    parser = argparse.ArgumentParser(description='Record data value changes')
    parser.add_argument('range', type=int, help='range of values to record')
    parser.add_argument('time', type=int, help='time to update values in seconds')
    return parser.parse_args()


def get_range_list(amount, val, end):
    return [
        ('flcon1:DataValue~Osiris_Test_Data_' + str(i + 1) + end, randint(0, val))
        for i in xrange(amount)
    ]


def get_time_list(amount, end):
    return [
        ('flcon1:DataValue~Osiris_Test_Data_' + str(i + 1) + end, time.strftime('%m/%d/%Y %H:%M:%S'))
        for i in xrange(amount)
    ]


def main():
    args = get_args()
    print('Logging test harness value changes')

    t0 = time.clock()
    value_list = get_range_list(args.range, 9, '.Value')
    time_list = get_time_list(args.range, '.TimeStamp')

    print(value_list)
    print(time_list)

    print('Wrote values')

    with open(str(args.range) + '.' + str(args.time) + '_1-iccp_harness.log', 'a') as f:
        for i in xrange(0, args.range):
            f.write('Osiris_Test_Data_' + str(i + 1) + ', realQTimetagExtended' + 
                    ', %g, %s, %s\n' % (value_list[i][1], 00, time_list[i][1]))

    t1 = time.clock()
    print t1-t0

    print('Logged values')


if __name__ == '__main__':
    main()


Result (the relevant parts):

Wrote values
7.145332
Logged values
         5001665 function calls (5001624 primitive calls) in 15.432 seconds

   Ordered by: internal time

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1   11.660   11.660   15.299   15.299 CR_135184.py:27(main)
  1000000    1.269    0.000    1.269    0.000 {time.strftime}
  1000000    0.876    0.000    0.925    0.000 random.py:175(randrange)
        1    0.551    0.551    1.708    1.708 CR_135184.py:13(get_range_list)
        1    0.510    0.510    1.779    1.779 CR_135184.py:20(get_time_list)
  1000000    0.232    0.000    1.157    0.000 random.py:238(randint)
  1000000    0.151    0.000    0.151    0.000 {method 'write' of 'file' objects}
        1    0.120    0.120   15.432   15.432 CR_135184.py:1(&lt;module&gt;)
  1000000    0.049    0.000    0.049    0.000 {method 'random' of '_random.Random' objects}


Basically, you're slowing down your code by checking the time. The generating of random numbers takes some time, but get_range_list and get_time_list are surprisingly fast.

The real bottleneck? Your OPC connection. And I'm not sure whether this can be fixed at all in code.