You need to change that in the calendar-portlet files.
E.g. have a look at calendar-full-portlet.tcl, you'll find this code snippet:
if {$view == "list"} {
set sort_by [ns_queryget sort_by]
set thirty_days [expr 60*60*24*30]
set start_date [ns_fmttime [expr [ns_time] - $thirty_days] "%Y-%m-%d 00:00"]
set end_date [ns_fmttime [expr [ns_time] + $thirty_days] "%Y-%m-%d 00:00"]
set cal_stuff [calendar::list_display \
-item_template $item_template \
-date $current_date \
-start_date $start_date \
-end_date $end_date \
-calendar_id_list $list_of_calendar_ids \
-sort_by $sort_by \
-url_template "?view=list&sort_by=\$order_by&page_num=$page_num" \
-url_stub_callback "calendar_portlet_display::get_url_stub" \
-show_calendar_name_p $show_calendar_name_p]
}
Change the end_date creation to whatever you want.
In what is DotLrn alpha (or beta?) there's a field "Show the next xxx days" that lets you choose how many days you want. May make sense to store that as a calendar-portlet parameter - but that is more like 5.1.
