TL;DR – You can vary the HIT Focus Duration while in Continuous mode and/or vary the execution of XMB at the same Focus Duration.
In XATA Continuous mode you control the default XSS target by the Athlete Type/Focus you select under Settings. But you can vary Focus when you select on-the-fly from the Training page or assign a workout to the Planner.
For example, let’s say I am using XATA Continuous, GC Specialist/8-minute Power with a Maintenance Improvement Rate. If I don’t switch things up, the HIT target on fresh days will always be close to that spec. However, I can vary the XMB execution (see below) or I can select a different Focus workout using Filter and set that as today’s target from the Training page with Play Now or schedule a workout to the Planner with a different Focus. XMB will use that XSS ratio as the target instead of the default advice for the day.
I can also adjust Athlete Type under Program settings if I want to perform my own periodization schedule. For example, X weeks at 20-minute power (mostly endurance) then X weeks at GC Specialist/8-minute, insert a rest week, then X weeks at Puncheur/4-minute as my final goal.
Regardless of what Athlete Type I select in Continuous mode, or what the advice is for the day, I’ll occasionally insert a sprint workout into my schedule. That can be as simple as riding easy for 5 or more minutes with 20-30 second sprints sprinkled in until the sprint effort begins to degrade (done for the day).
If you play around with the XMB Workout Generator you’ll notice interval duration increases with a rise in CL. For example, 16 sec @500 watts at CL2 isn’t 16 secs at CL8. That’s not obvious unless you zoom in and hover on an interval. The micro-interval format remains but 16 sec isn’t a fixed value. You can also edit interval duration directly on the Workout Generator using the slider (up to 2 min). The interval count, MPA drawdown, rest-in-between, workout duration, and Difficulty level change accordingly.
Try the XMB Workout Generator and watch what happens to the chart if you double the default seconds versus increasing CL.
While the MB Generator tab creates a structured workout to follow there’s nothing stopping you from performing ad hoc longer intervals while free riding with XMB.
For example, tackle a traditional VO2max set with a watt target in the 105-125%TP range for 2+ minutes. You’ll be ignoring XMB guidelines, but the buckets will fill regardless.
I’d argue XMB can actually assist you with organically performing VO2max intervals.
The goal isn’t a strict watt target for X minutes but reaching a physiological state and holding it there to the best of your ability. Between the XMB rainbow arcs, CL gauge, interval timer, and HR field you have everything required to quantify that effort and repeat it.
Micro-intervals will also drive you into a VO2max state as long as you push to the CL required and repeat that effort with short recoveries.
When you closely adhere to XMB default guidelines for target watts, interval duration, and recovery countdown, all three buckets fill at the same rate in line with estimated activity time. However, you can shorten that time estimate and reduce interval count by increasing interval duration and complete the high/peak portion of the workout sooner.
You can also front load or back load the interval portion of a ride.
IMO the best way to learn XMB is to ride indoors without a workout selected and experiment on HIT days.
You can vary the execution of the workout to reach today’s goal. This becomes most evident the more you play with XMB and draw outside the lines.
Don’t want to do 23 micro intervals today? Shoot for 15 instead. Or go long at lower watts if up for a traditional VO2max challenge. Or go short and spiky and make it a sprint day.
XMB gamifies the process however you decide to fill the buckets. 
