this example might help you.
using Gnuplot, TimeSeries, MarketData, Dates
# dummy data
dates = Date(2018, 1, 1):Day(1):Date(2019, 12, 31)
ta = TimeArray(dates, rand(length(dates)))
timefmt = "%Y-%m-%d" # hour:minute:seconds are also available
pfmt = "%Y-%m-%d"
rot_xtics = -35
vals = 0.5*values(ta)
tempo = string.(timestamp(ta))
xmin1 = "2018-02-01"
xmax1 = "2019-04-01"
@gp "set xdata time" "set timefmt '\"$(timefmt)\"'" "set grid" :-
@gp :- "set format x '$(pfmt)'" "set xtics rotate by $(rot_xtics)" :-
@gp :- "set tmargin at screen 0.96; set bmargin at screen 0.15" :-
@gp :- "set lmargin at screen 0.1; set rmargin at screen 0.96" :-
@gp :- """set xrange [\'"$(xmin1)\"':\'"$(xmax1)\"']""" yrange = (-0.25,0.75) :-
@gp :- tempo vals "u 1:2 w l lc 'black' t 'series'"
A comple set of examples doing dates can be found here
the main file with all predefined functions is here
https://cdn.nextjournal.com/data/Qmdk7ZYTeibg3XnaDWHXG4hamxYPoqwt2MuDEjwFkdsz4R?filename=plotMarketData.jl&content-type=
but probably the first example will be enough.