I've put together a playlist that can be adapted to your needs. This is a playlist where Spandau Ballet's Gold is playing around the finish time you are looking for
Elapsed/ Track length/ Track
00:05:03Mr Blue Sky
0:07:5900:02:56Cant hurry love
0:10:4100:02:42There she goes
0:15:2100:04:40you can call me Al
0:19:0000:03:39I'm gonna be
0:22:5900:03:59Walking on Sunshine
0:26:5000:03:51Gold
0:31:0200:04:12Every Breath you take
0:35:2500:04:23What have I done to deserve this
Just move Gold down to 7th for 30 mins and 8 for 35 mins.
Clearly you can put in your own tracks but using the timings to have a motivating song at the right time seems useful. The theme from Chariots of Fire is obviously another suggestion.
Based on the 25 minute time Spandau Ballet should kick in with 400m to go, 30 minute with 200m to go and 35 minutes about 100m to go
Just a thought.