Maybe a sort of three tiered defense? The main line, maybe within a minute to fifteen seconds of the seed. Fuzzy number there because it's a bit hard to get a feel for big a radius a solid defensive line could be formed at with these forces. Some room to fall back, but able to respond quickly if anyone slips through the lines and makes a break for the seed.
A force right
at the seed, able to deal with (or at least stall long enough to receive backup) anyone who gets through the main line undetected or too quickly for the defenders to catch. They'd also be reserves for the main line, as well as their final fallback position. Info Team would probably be stationed here so they don't have to split their attention between fighting for their lives and coordinating the battle.
Finally, a skirmishing force can engage the enemy on their advance into the town before they meet the main line. Locate the enemy, get a hit in, and disengage quickly. Disorganize the enemy and inflict some light casualties on them before they reach the main line. They'd also be able to alert everyone as to the specific angles the Glow is approaching from, and when. The Glow will hit the main line on Mitakihara's terms, not theirs. During the main battle these elements would either join the main line or remain as flanking elements and/or calvary analogues, sort of like Jonen C suggested last page.
I do think the main line not being right at the seed is important. Like, that does make Rin slipping past them possible, but the reserves at the seed and positioning the main line close enough to be able to respond quickly should all but eliminate that, and drawing the line right at the seed means that if the enemy breaks through
anywhere, there's virtually no ability to recover from it.
If there's any info team members with powers good for scouting that need line of sight or proximity or somesuch, if might be good to have them accompany skirmish teams.
Let me put it this way: While I don't think it's actively counterproductive, is it a good use of our very limited remaining preparation time?
Probably. It's not the sort of preparations where nearly everyone is doing something at all times. They're magi defending a town, not a modern military preparing for mobilization. There's no equipment to prepare, no supply lines to establish. I'd expect a decent amount of idle hands from the people who aren't doing the planning or helping manage the evacuation.
Less pragmatically, it could save lives on both sides, so yes, I think it's worth it.