Convert string column to Datetime

You can iterate through the rows of that dataset converting date strings to dates something like this:

# Create sample dataset with date strings.
headers = ['DateTime', 'Value']
data = [['2019-02-27 22:57:00.0000000',72181]]
data.append(['2019-02-28 22:57:00.0000000', 73365])
data.append(['2019-03-01 22:57:00.0000000', 73905])
dataset = system.dataset.toDataSet(headers, data)
# Convert date strings in first column to dates in new dataset.
newData = []
print 'Original rows:'
for row in range(dataset.rowCount):
	print type(dataset.getValueAt(row, 0)), dataset.getValueAt(row, 0), dataset.getValueAt(row, 1)
	# Make new row with date string converted to date.
	newData.append([system.date.parse(dataset.getValueAt(row, 0)), dataset.getValueAt(row, 1)])
newDataset = system.dataset.toDataSet(headers, newData)
# Confirm types are dates.
print 'Converted rows:'
for row in range(newDataset.rowCount):
	print type(newDataset.getValueAt(row, 0)), newDataset.getValueAt(row, 0), newDataset.getValueAt(row, 1)
# Write/assign newDataset to chart data.

Which gives this output in script console:

Original rows:
<type 'unicode'> 2019-02-27 22:57:00.0000000 72181
<type 'unicode'> 2019-02-28 22:57:00.0000000 73365
<type 'unicode'> 2019-03-01 22:57:00.0000000 73905
Converted rows:
<type 'java.util.Date'> Wed Feb 27 22:57:00 PST 2019 72181
<type 'java.util.Date'> Thu Feb 28 22:57:00 PST 2019 73365
<type 'java.util.Date'> Fri Mar 01 22:57:00 PST 2019 73905