Have you timed it? A full 3/4 of a minute is an excessively long time for the unit to light up and stabilize the temp- it's typically 2-4 seconds from start of flow to ignition & temp stabilization with almost any tankless. Even starting with room-temp water in the pipes, at 2gpm flow that's enough to get hot water from the unit at 100 feet of distribution plumbing away. Fully 45 seconds may be an indication that it's having startup problems that should be addressed.
That said, many water-sipping newer appliances only fill in short bursts of a quart or two at a time. If these bursts are less than 5-10 seconds long, the first couple of seconds of flow is letting cold water through the HW heater during it's ignition cycle, so the distribution plumbing will have segments of both hot & cold water (referred to as the "cold water sandwich"), which means the fill-water at the appliance is tepid, not full-hot.
A common solution is a recirculation system with a pump that purges the hot water distribution plumbing of cold water when a sensor senses flow, or a switch is pressed to call hot water, like the Metlund D'Mand systems you mention. Some others use timers, or always maintain hot water in the plumbing, but those can waste a lot of energy in standby mode, but the demand-sensing systems like the Metlund don't. Rather than wasting energy by dumping room-temp water or tepid water down the drain until the hot water arrives, the demand systems circulate the water in the distribution line back to the cold-water input to the tankless, so the tankless only needs to raise the temp from 65-90F to 120F instead of from 40-50F to 120F. This is a significant fraction of the total, saving both water and energy. Also, since they purge the entire volume of the intervening plumbing of room temp or tepid water with each cycle it runs the tankless closer to it's steady-state efficiency, which is much more efficient than multiple short-cycling bursts. As long as it's a demand-triggered pump (either button-actuated by the user or a flow sensor), recirculation systems are either neutral, or increasing the net efficiency of the system while guaranteeing that your getting hot, not tepid water. See: http://www.gothotwater.com/D%27MAND/DOE/default.htm
The system efficiency can be further improved at low cost by insulating the distribution plumbing, preferably with 3/4" wall closed cell foam (not the cheaper 3/8" stuff found at big blue or orange box stores.) By reducing the rate of heat lost from the hot water abandoned in the plumbing, subsequent draws are often still hot enough to be useful (or with a recirc system, hot enough that it inhibits the pump operation). If your plumbing supply outlets don't have it in stock, Grainger often does, or it can be ordered online from any number of vendors (be sure to get the right diameter for your plumbing). Something like 15% of the total energy in a hot water system is wasted in distribution losses in typical homes. Insulating the pipes can bring that down to low-mid single-digits.
But use a watch to time how long it's REALLY taking hot water to get to the tap to the heater from a cold start. If it's as long as you say it is, there could be some maintenance or installation issues to sort out. Alternatively, measure the volume that would be going down the drain before the first hot water arrives, and estimate the length/size of plumbing between the heater and the tap. It takes about 100' of half-inch plumbing to hold a gallon of water, or 50' of 3/4". If you only have 15-20 feet of line between the heater and the tap it should be well UNDER a gallon of flow before the water is warming significantly at the tap, full temp shortly thereafter.