Assuming your _time fields are already align or binned to the minute and are in ascending order, try something like this:
| streamstats range(_time) as previous_gap window=2
| reverse
| streamstats range(_time) as next_gap window=2
| where previous_gap != 60 OR next_gap != 60
| streamstats current=f window=1 values(_time) as latest
| where next_gap=60
| reverse
| rename _time as earliest
| fields earliest latest
| fieldformat earliest=strftime(earliest,"%F %T")
| fieldformat latest=strftime(latest,"%F %T")
