web/project_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>

        <record id="view_task_timeline" model="ir.ui.view">
            <field name="name">project.task.timeline</field>
            <field name="model">project.task</field>
            <field name="type">timeline</field>
            <field eval="2" name="priority"/>
            <field name="arch" type="xml">
                <timeline date_start="date_start" 
                          date_stop="date_end"
                          date_delay='1'
                          string="Tasks"
                          default_group_by="user_id" event_open_popup="true" colors="#ec7063:user_id == false;#2ecb71:kanban_state=='done';">
                </timeline>
            </field>
        </record>

        <record id="action_view_task" model="ir.actions.act_window">
            <field name="name">Tasks</field>
            <field name="res_model">project.task</field>
            <field name="view_mode">kanban,tree,form,calendar,gantt,timeline,graph</field>
            <field name="search_view_id" ref="project.view_task_search_form"/>
            <field name="inherit_id" ref="project.action_view_task"/>
        </record>
    </data>
</openerp>