Short answer - no you cannot have both, and if you do, the 'span' will win.
The longer answer is that technically you can 'bin' other fields besides time. In the timechart below, im setting a span for the _time, but note the bins=3. That is actually telling timechart to bin the date_hour values into numeric ranges.
index=_internal source=*metrics.log group=per_index_thruput series!=_internal | timechart span=1h sum(kb) by date_hour bins=3
You know what's awesome when you bin fields other than time? logarithmic spans: `index=weblogs | bin responseTime span=1.2log1.6 | stats count by responseTime