3Com 8807 Command Reference Manual page 497

Use the undo
timer spf
command to restore the system default value.
In IS-IS, when the LSDB of the corresponding level is changed, SPF calculation is
required. However, if the SPF calculation is performed too frequently, the system
efficiency will be lowered. By setting a proper interval for performing SPF
calculation, you can avoid the above situation. This setting can be made according
to actual conditions.
Example
# Set the SPF calculation interval of the router to 3, 100 and 500 seconds.
[3Com-isis] timer spf 3 100 500