2-3 hours build needs a lot of experience building these models as well as materials to complete a Leading Edge design.
OK, if goal is 45 seconds, take that design and SIMPLIFY.
Select fairly light balsa, say 7-8 lb/ft3.
Reduce wing size to 10 cm chord. Use 3/32 by 1/16 inch sticks on edge for spars. Same for ribs, don''t worry about curve. Don't use fins, crack the spars and kick up the outer 10 cm of each tip by 3 cm or so. Glue cracked spars to lock in dihedral. Cover with light tissue or light plastic grocery bags.
Glue a 1/8 by 1/4 hard balsa stick along the chord 1 cm to right of center line so it sticks out beyond wing about 1 cm. Glue a 1/8 inch riser under the leading edge. Make sure the wing is flat or left leading edge is twisted higher than right a little. NOT the right leading edge higher than left.
Tail, build a flat rectangle 5 cm longer than the max span the rules allow by say 5-6 cm chord. Again, build it flat, but with 1/16 inch square. Cover same as wing. Crack the spars and kick up the outer 2.6 cm of both tips by 90 degrees.
Motor stick, 10 inchs long by 1/4 by 3/8 light balsa. Tail boom 8-12 inches 1/4 by 1/8 tapering to 1/8 by 1/8. Offset tip of tailboom to centerline of motorstick about 1/2 inch to the left. Add tail hook and prop hanger, reinforce with thread wrapping coated by glue.
Glue the rear stab on with a 1/16 inch riser under the rear spar. Make sure it tilts to the right so left tip is 1/2 or so higher than right.
Attach wing to motor stick with dental bands front and back. Slide wing to balance with prop, motor, everything at about the rear spar to start.
Test glide with a couple hundred winds in a 3/32 1.5 gm motor. It should fly level with a slight descent. If stalling move wing back. If diving, move wing forward or raise leading edge by wedging a piece of wood under the attachment stick at front. Add winds to start climbing. WIND it. Lube your motors.
If you are under 10 grams and trim it right, such a plane can hit 45 seconds. With two days, your goal should be to finish your plane and trim it well enough to fly at least level in a 30 foot diameter circle. Any more is gravy in that short time, unless you have a mentor on hand.
Oh, and spend some time reading the 800 or so messages in this forum.