If we convert the percentages into numbers of students, including the margin of error:
Group 1: 40-49 (earlier) (31%-39%)
Group 2: 21-30 (same) (16%-24%)
Group 3: 45-55 (later) (35%-43%)
Group 4: 3-12 (no opinion) (2%-10%)
Interval estimate for group 1 is 40-49 students, and for group 3 is 45-55 students. The earlier group 1 could persuade the no opinion group 4 to join them. This would change the interval to 43-61, compared to 45-55 for group 3. In percentages this comes to 34%-47% approx.
