[solved] why the sketchpad last longer than I set?

In my experiment, I set the sketchpad to show stimulus for 600ms, and the keyboard_response has a timeout of 2000ms. I put the keyboard_response next to the sketchpad. However, the sketchpad last obviously longer than 600ms, probably for 2600ms if I does not press any key. While if I press one key after 600ms, the sketchpad disappears at once; but if I press the key within 600ms, the stimulus last for about 2600ms again. I intended to let the stimulus display with a constant period and disappear regardless the response time. So what's the problem here? How could I do that? The codes are as follows. Thanks.

# Generated by OpenSesame 0.27.3 (Frisky Freud)
# Tue Mar 04 14:43:25 2014 (nt)
# <http://www.cogsci.nl/opensesame>

set mouse_backend "xpyriment"
set subject_parity "even"
set height "800"
set sound_buf_size "512"
set font_italic "no"
set custom_cursor "no"
set canvas_backend "xpyriment"
set synth_backend "legacy"
set sound_channels "2"
set title "Attentional capture for Android"
set psychopy_waitblanking "yes"
set coordinates "relative"
set start "experiment"
set sampler_backend "legacy"
set sound_sample_size "-16"
set font_family "sans"
set foreground "white"
set font_bold "no"
set sound_freq "48000"
set description "An attention capture paradigm, modified for the Android runtime"
set psychopy_monitor "testMonitor"
set background "black"
set font_size "18"
set enable_escape "no"
set keyboard_backend "legacy"
set transparent_variables "no"
set compensation "0"
set subject_nr "0"
set width "1280"

define sequence sequence
    run reset_feedback "always"
    run _loop "always"
    run _feedback "always"

define sequence _sequence
    run fixation_dot "always"
    run sketchpad "always"
    run keyboard_response "always"
    run logger "always"

define feedback _feedback
    set duration "keypress"
    set reset_variables "yes"
    set description "Provides feedback to the participant"
    draw textline 0 -128 "本部分结束" center=1 color=white font_family="sans" font_size=18 font_italic=no font_bold=no show_if="always"
    draw textline 0 -64 "你的反应时为[avg_rt]ms" center=1 color=white font_family="sans" font_size=18 font_italic=no font_bold=no show_if="always"
    draw textline 0 0 "你的正确率为[acc]%" center=1 color=white font_family="sans" font_size=18 font_italic=no font_bold=no show_if="always"
    draw textline 0 64 "按空格键继续..." center=1 color=white font_family="sans" font_size=18 font_italic=no font_bold=no show_if="always"

define loop _loop
    set repeat "2"
    set description "Repeatedly runs another item"
    set item "_sequence"
    set column_order "stimulus;correct_response"
    set cycles "2"
    set order "random"
    setcycle 0 stimulus "上"
    setcycle 0 correct_response "f"
    setcycle 1 stimulus "下"
    setcycle 1 correct_response "j"
    run _sequence

define sketchpad end_of_practice
    set duration "keypress"
    set description "Tell the participant that the practice phase is finished"
    set start_response_interval "no"
    draw textline 0 -64 "The practice phase is finished" center=1 color=white font_family="sans" font_size=18 font_italic=no font_bold=no show_if="always"
    draw textline 0 64 "Tap the screen to start the real experiment ..." center=1 color=white font_family="sans" font_size=18 font_italic=no font_bold=no show_if="always"

define sequence experiment
    set description "The main experimental sequence"
    run text_display "always"
    run _text_display "always"
    run loop "always"
    run end_of_practice "always"

define fixation_dot fixation_dot
    set foreground "white"
    set style "cross"
    set description "Presents a central fixation dot with a choice of various styles"
    set duration "1700"
    set background "black"
    set y "0"
    set x "0"
    set penwidth "4"

define logger logger
    set description "Logs experimental data"
    log "display_size"
    log "distractor"
    log "practice"
    log "condition"
    log "response"
    log "correct"
    log "response_time"

define text_display text_display
    set foreground "white"
    set font_size "36"
    set description "Presents a display consisting of text"
    set maxchar "50"
    set align "center"
    __content__

    欢迎参加实验！

    请仔细阅读接下来的实验说明。
    如有任何疑问，请及时联系主试人员。


    按空格键继续
    __end__
    set background "black"
    set duration "keypress"
    set font_family "sans"

define text_display _text_display
    set foreground "white"
    set font_size "36"
    set description "Presents a display consisting of text"
    set maxchar "50"
    set align "center"
    __content__

    练习一

    请对屏幕中央的文字做按键反应。

    如果看到了“上”，请左手食指按“F”键；
    如果看到了“下”，请右手食指按“J”键。

    请做到又快又准确的按键。

    明确了按空格键继续。
    __end__
    set background "black"
    set duration "keypress"
    set font_family "sans"

define sketchpad sketchpad
    set duration "600"
    set description "Displays stimuli"
    draw rect -100 -100 200 200 fill=1 penwidth=1 color=grey show_if="always"
    draw textline 0 0 "[stimulus]" center=1 color=red font_family="sans" font_size=54 font_italic=no font_bold=yes show_if="always"

define keyboard_response keyboard_response
    set description "Collects keyboard responses"
    set timeout "2000"
    set flush "yes"

define reset_feedback reset_feedback

define loop loop
    set repeat "1"
    set description "Repeatedly runs another item"
    set item "sequence"
    set column_order "practice"
    set cycles "1"
    set order "random"
    setcycle 0 practice "yes"
    run sequence