I'm on my fourth batch of IPA from a "tried & true" recipe from a local brewshop. On the first three, I transferred from Primary to Secondary after the bubbles got to more than 1 minute intervals, which always happened by 7-8 days. This batch though is now on day 16 and I'm still at a 45-50 second interval. Also this batch took a good day to get up to speed with the fermentation -- slower than usual. The only environmental difference that I can think of is that it's warmer now than the previous batches, but not substantially so.
Should I really worry?